Stockholders' Equity - Shares Repurchased (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Number of shares repurchased	3,979,170	525,504	7,040,621
Average price per share	$ 109.64	$ 85.27	$ 76.26
Total cost of repurchases	$ 436,369	$ 44,822	$ 537,088