Quarterly Financial Data -- Unaudited (Details) - USD ($) $ / shares in Units, $ in Thousands |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2018 |
Sep. 30, 2018 |
Jun. 30, 2018 |
Mar. 31, 2018 |
Dec. 31, 2017 |
Sep. 30, 2017 |
Jun. 30, 2017 |
Mar. 31, 2017 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Quarterly Financial Information Disclosure [Abstract] | |||||||||||
| Total revenue | $ 1,495,908 | $ 1,467,383 | $ 1,432,299 | $ 1,375,102 | $ 1,403,898 | $ 1,379,596 | $ 1,347,569 | $ 1,294,066 | $ 5,770,692 | $ 5,425,129 | $ 5,017,220 |
| Cost of services | (572,551) | (564,735) | (636,668) | (534,652) | (572,405) | (519,024) | (513,446) | (497,107) | |||
| Income from operations | 459,173 | 482,557 | 361,627 | 423,591 | 396,706 | 433,965 | 416,353 | 393,840 | 1,726,948 | 1,640,864 | 1,432,129 |
| Net income | $ 251,052 | $ 343,048 | $ 292,352 | $ 289,441 | $ (36,996) | $ 275,722 | $ 202,109 | $ 207,073 | $ 1,175,893 | $ 647,908 | $ 745,933 |
| Net income (loss) per common share--basic (in dollars per share) | $ 0.06 | $ 0.08 | $ 0.07 | $ 0.06 | $ (0.01) | $ 0.06 | $ 0.04 | $ 0.04 | $ 0.26 | $ 0.14 | $ 0.15 |
| Net income (loss) per common share--diluted (in dollars per share) | $ 0.06 | $ 0.07 | $ 0.06 | $ 0.06 | $ (0.01) | $ 0.06 | $ 0.04 | $ 0.04 | $ 0.26 | $ 0.14 | $ 0.15 |
| X | ||||||||||
- Definition The aggregate cost of services rendered during the reporting period, excluding depreciation, depletion and amortization. No definition available.
|
| X | ||||||||||
- Definition The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- Definition The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/exampleRef
|
| X | ||||||||||
- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- Definition The net result for the period of deducting operating expenses from operating revenues. No definition available.
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|