Share Repurchase Programs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Repurchase Programs (Textual) [Abstract]
Common stock repurchases	$ 78,316	$ 37,274	$ 6,141
December 2013 Anti-Dilutive Share Repurchase Program
Share Repurchase Programs (Textual) [Abstract]
Common stock repurchases	$ 78,000	$ 37,000	$ 6,000
Common Stock
Share Repurchase Programs (Textual) [Abstract]
Repurchased and retired shares (in shares)	1,086,901	536,298	69,107
Common stock repurchases	$ 543	$ 268	$ 35
December 2015 Program
Share Repurchase Programs (Textual) [Abstract]
Maximum number of share repurchases authorization (in shares)			1,500,000.0