Earnings Per Share Summary (Details) (USD $) In Thousands, except 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 attributable to common shareholders	$ 19,523	$ 35,356	$ 25,896	$ 64,317
Less: adjustment for income allocated to participating securities	(2,683)	(127)	(3,543)	(243)
Net income attributable to common stockholders - basic and diluted	$ 16,840	$ 35,229	$ 22,353	$ 64,074
Weighted average common shares outstanding - basic	86,887	87,865	87,559,000	87,823,000
Plus: dilutive effect of stock options and unvested restricted stock units	912	972	1,314,000	945,000
Weighted average common shares outstanding - diluted	87,799	88,837	88,873,000	88,768,000
Basic	$ 0.19	$ 0.40	$ 0.26	$ 0.73
Diluted	$ 0.19	$ 0.40	$ 0.25	$ 0.72