Shareholders' Equity (Earnings Per Share Reconciliation) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net income	$ 229,484	$ 237,951	$ 183,684
Preferred Stock dividends	5,876	5,876	5,337
Less: Net income allocated to participating shareholders	1,836	1,930	1,545
Net income attributable to common shareholders	$ 221,772	$ 230,145	$ 176,802
Weighted average number of common shares outstanding - basic	165,669	165,296	149,607
Basic earnings per common share	$ 1.34	$ 1.39	$ 1.18
Weighted average number of common shares outstanding - basic	165,669	165,296	149,607
Employee stock award plans	166,127	166,054	150,421
Diluted earnings per common share	$ 1.33	$ 1.39	$ 1.18
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock award plans	458	758	814