Acquisitions and Dispositions - KLAS - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended								11 Months Ended	12 Months Ended
	Feb. 13, 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	Dec. 31, 2014
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
KLAS [ Member]
Business Acquisition [Line Items]
Purchase price of entities acquired	$ 150,800
Acquisition related costs													$ 100	$ 100
Acquisition date	Feb. 13, 2015
Revenue included in consolidated statements of operations and comprehensive income										$ 32,700
Operating income (loss)										$ 6,600