Repurchases of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Shares of common stock repurchases authorized (in shares)	68,000,000
Remaining shares available for repurchase under authorization (in shares)	3,200,000
Share repurchased during the period (in shares)	1,773,000	1,749,000	3,071,000
Shares acquired through employee surrender for statutory tax withholding (in shares)	52,000	57,000	60,000
Total shares repurchased (in shares)	1,825,000	1,806,000	3,131,000
Cost of share repurchased in the open market	$ 368,691	$ 270,297	$ 313,072
Cost of shares for employee surrenders	9,375	8,074	4,372
Total cost of shares	$ 378,066	$ 278,371	$ 317,444
Average cost per share - open market repurchases (in USD per share)	$ 207.92	$ 154.51	$ 101.96
Average cost per share - employee surrenders (in USD per share)	182.18	142.55	73.04
Average cost per share - total (in USD per share)	$ 207.19	$ 154.13	$ 101.40