Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Feb. 28, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Treasury Shares			18,151,560	18,263,589
Additional authorized shares purchased			10,496,421
Common stock repurchased (in shares)	1,000,952	3,502,627
Preferred stock, authorized (in shares)			1,000,000
Preferred stock, issued (in shares)			0
Stock repurchased during period		$ 125,000
Percent of shares authorized for repurchase		80.00%
Share repurchases, effective average price per share (in dollars per share)	$ 27.76
Treasury Stock
Class of Stock [Line Items]
Repurchased shares		$ 100,000		$ 25,000	$ 100,000
Share repurchases, price paid per share (in dollars per share)		$ 28.55
Additional Paid-in Capital
Class of Stock [Line Items]
Repurchased shares				$ (25,000)	$ 25,000
Nonvoting Common Stock
Class of Stock [Line Items]
Common stock repurchased (in shares)			0	1,000,952	3,502,627