Consolidated Statements of Cash Flows - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income		$ 24,047	$ 147,284	$ 47,451
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, accretion, and amortization		721,970	697,078	672,113
Non-cash asset impairment and decommission costs		39,501	32,241	26,192
Non-cash compensation expense		68,890	73,214	42,327
Loss (gain) on remeasurement of U.S. denominated intercompany loans		220,354	(13,134)	89,101
Loss from extinguishment of debt, net		17,838	235	14,087
Deferred income tax (benefit) expense	[1]	(63,187)	15,935	(15,287)
Amortization of deferred financing fees		20,058	20,358	20,289
Non-cash interest expense	[1]	24,870	3,193	2,640
Other non-cash items reflected in the Statements of Operations	[1]	2,979	(1,888)	(1,388)
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable and costs and estimated earnings in excess of billings on uncompleted contracts, net		38,195	(12,146)	(29,427)
Prepaid expenses and other assets		2,614	878	(38,040)
Operating lease right-of-use assets, net		109,935	93,665
Accounts payable and accrued expenses		13,173	(5,951)	(3,021)
Long-term lease liabilities		(100,847)	(87,544)
Other liabilities		(14,357)	6,627	23,581
Net cash provided by operating activities		1,126,033	970,045	850,618
CASH FLOWS FROM INVESTING ACTIVITIES:
Acquisitions		(271,418)	(773,957)	(451,829)
Capital expenditures		(128,566)	(154,236)	(149,812)
Purchase of investments		(1,288,705)	(638,963)	(156,983)
Proceeds from sale of investments		1,239,206	625,807	150,890
Other investing activities		3,117	(5,809)	(10,613)
Net cash used in investing activities		(446,366)	(947,158)	(618,347)
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings under Revolving Credit Facility		895,000	755,000	1,120,000
Repayments under Revolving Credit Facility		(1,005,000)	(590,000)	(835,000)
Repayment of Term Loans		(24,000)	(24,000)	(1,947,000)
Proceeds from issuance of Term Loans, net of fees				2,377,218
Proceeds from issuance of Senior Notes, net of fees		1,479,484
Repayment of Senior Notes		(759,143)
Proceeds from issuance of Tower Securities, net of fees		1,335,895	1,152,458	631,466
Repayment of Tower Securities		(1,200,000)	(920,000)	(755,000)
Termination of interest rate swap		(176,200)
Repurchase and retirement of common stock		(859,335)	(466,982)	(795,581)
Payment of dividends on common stock		(207,689)	(83,387)
Proceeds from employee stock purchase/stock option plans, net of taxes		54,049	116,202	59,880
Other financing activities		(2,078)	(1,605)	(4,520)
Net cash used in financing activities		(469,017)	(62,314)	(148,537)
Effect of exchange rate changes on cash, cash equivalents, and restricted cash		(8,962)	2,247	(9,729)
NET CHANGE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH		201,688	(37,180)	74,005
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH:
Beginning of year		141,120	178,300	104,295
End of year		342,808	141,120	178,300
Cash paid during the period for:
Interest		351,886	386,615	376,628
Income taxes		20,275	21,598	21,645
SUPPLEMENTAL CASH FLOW INFORMATION OF NON-CASH ACTIVITIES:
Right-of-use assets obtained in exchange for new operating lease liabilities		78,674	175,517
Operating lease modifications and reassessments		(10,550)	(52,383)
Right-of-use assets obtained in exchange for new finance lease liabilities		1,087	$ 3,499	$ 1,039
Common stock issued in connection with acquisitions			1,680
Consolidation of an equity method investment			$ 71,990
Deferred payment on acquired assets		$ 77,124

[1] Certain reclassifications of the prior years’ amounts have been made to conform to the current year’s presentation.