Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 133,097	$ 156,937	$ 181,640
State	24,944	34,927	36,281
Foreign	27,079	20,725	13,892
Deferred:
Federal and state	41,717	(3,785)	(8,398)
Foreign	95	1,917	(181)
Provision (benefit) for income taxes	$ 226,932	$ 210,721	$ 223,234