Acquisitions and Dispositions - Kixer - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended									12 Months Ended
	Oct. 01, 2015	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Revenue included in consolidated statements of operations and comprehensive income		$ 653,664	$ 611,870	$ 626,115	$ 540,317	$ 309,879	$ 275,659	$ 261,994	$ 255,658		$ 2,431,966	$ 1,103,190	$ 896,377
Operating income (loss)		$ 140,837	$ 129,072	$ 138,685	$ 110,151	$ 92,475	$ 72,897	$ 64,007	$ 57,929		518,745	287,308	206,107
Remaining Earnout payment												4,044
Payments for Contingent Consideration											$ 263,647
Kixer [Member]
Business Acquisition [Line Items]
Acquisition date	Oct. 01, 2015
Cash paid in business acquisition	$ 8,500
Maximum Earnout payment	$ 7,000
Acquisition related costs													100
Revenue included in consolidated statements of operations and comprehensive income										$ 1,700
Operating income (loss)										$ 400
Remaining Earnout payment												4,000
Payments for Contingent Consideration												$ 2,000
Kixer [Member] | Carrying Reported Amount Fair Value Disclosure [Member] | Level 3 [Member]
Business Acquisition [Line Items]
Fair Value of Earnout Payment													$ 3,000