Summary of Significant Accounting Policies Summary of Significant Accounting Policies, Revenue Recognition (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 850,760		$ 769,241		$ 812,572		$ 798,212		$ 820,814		$ 778,786		$ 796,092		$ 794,482		$ 3,230,785	$ 3,190,174	$ 3,095,031
Gross profit	217,868		159,732		191,146		191,834		210,263		166,170		188,127		195,762		760,580	760,322	722,779
Costs of revenue	(632,892)		(609,509)		(621,426)		(606,378)		(610,551)		(612,616)		(607,965)		(598,720)		(2,470,205)	(2,429,852)	(2,372,252)
Corporate general and administrative expenses																	(126,886)	(145,596)	(158,651)
Gains on divestitures and impairment charges, net																	32,919	15,933	7,015
Operating income	240,945		128,585		150,105		146,978		172,710		132,303		161,954		163,692		666,613	630,659	571,143
Interest expense																	(185,843)	(181,556)	(169,125)
Losses on early extinguishment of debt, net																	16,637	10,131	274
Nonoperating Income (Expense)																	299	2,760	(1,486)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	195,172	[1]	72,869	[1]	96,083	[1]	100,308	[1]	126,012	[1]	86,036	[1]	119,315	[1]	110,369	[1]	464,432	441,732	400,258
Income Tax Expense (Benefit)	47,999		1,997		23,570		21,095		(67,224)		17,043		16,034		28,321		(94,661)	5,826	146,589
Net income	147,173		70,872		72,513		79,213		193,236		68,993		103,281		82,048		369,771	447,558	546,847
Net income attributable to noncontrolling interests	(21)		(80)		(184)		110		(190)		(58)		(42)		(60)		(175)	(350)	(184)
Net income attributable to common stockholders	$ 147,152		$ 70,792		$ 72,329		$ 79,323		$ 193,046		$ 68,935		$ 103,239		$ 81,988		$ 369,596	$ 447,208	$ 546,663
Net income attributable to common stockholders, basic	$ 0.81	[2]	$ 0.39	[2]	$ 0.40	[2]	$ 0.44	[2]	$ 1.07	[2]	$ 0.38	[2]	$ 0.57	[2]	$ 0.44	[2]	$ 2.03	$ 2.45	$ 2.91
Net income attributable to common stockholders, diluted	$ 0.79	[2]	$ 0.38	[2]	$ 0.39	[2]	$ 0.43	[2]	$ 1.04	[2]	$ 0.37	[2]	$ 0.55	[2]	$ 0.43	[2]	$ 1.99	$ 2.39	$ 2.84
Change in amounts due for unfulfilled performance obligations																	$ (10,223)	$ (546,554)	$ 0

[1] Includes Gains (losses) on divestitures and impairment charges, net, as described in Note 16.

[2] Net income per share is computed independently for each of the quarters presented. Therefore, the sum of the quarters’ net income per share may not equal the total computed for the year.