Shareholders' Equity - Share Repurchases (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure Shareholders Equity [Abstract]
Total number of shares repurchased and retired	2,908	2,179	554
Total investment	$ 245,816	$ 293,616	$ 81,812