Earnings Per Share Computation of Basic and Diluted Income Per Common Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 104,445	$ 84,682	$ 294,088	$ 213,228
Less: distributed and undistributed earnings allocated to participating securities	(1,451)	0	(4,381)	0
Net income attributable to common shareholders	$ 102,994	$ 84,682	$ 289,707	$ 213,228
Weighted average basic common shares outstanding	97,165	96,758	96,954	96,536
Effect of dilutive securities	57	839	53	976
Diluted common shares outstanding	97,222	97,597	97,007	97,512
Basic income per common share (in dollars per share)	$ 1.06	$ 0.88	$ 2.99	$ 2.21
Diluted income per common share (in dollars per share)	$ 1.06	$ 0.87	$ 2.99	$ 2.19