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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 99,557	$ 66,252	$ 189,643	$ 128,546
Less: distributed and undistributed earnings allocated to participating securities	(1,514)	0	(2,918)	0
Net income attributable to common shareholders	$ 98,043	$ 66,252	$ 186,725	$ 128,546
Weighted average basic common shares outstanding	96,906	96,432	96,847	96,424
Effect of dilutive securities	8	1,062	34	1,037
Diluted common shares outstanding	96,914	97,494	96,881	97,461
Basic income per common share	$ 1.01	$ 0.69	$ 1.93	$ 1.33
Diluted income per common share	$ 1.01	$ 0.68	$ 1.93	$ 1.32