Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income to common shareholders	$ 52,267	$ 46,907	$ 101,281	$ 50,746
Net income allocated to participating securities - basic and diluted	1,166	1,136	2,322	1,233
Net income allocated to common shareholders - basic and diluted	$ 51,101	$ 45,771	$ 98,959	$ 49,513
Weighted-average common shares - basic	84,614,000	77,523,000	84,489,000	77,512,000
Dilutive potential common shares	253,000	157,000	266,000	164,000
Weighted-average common shares - diluted	84,867,000	77,680,000	84,755,000	77,676,000
Earnings per common share: Basic	$ 0.60	$ 0.59	$ 1.17	$ 0.64
Earnings per common share: Diluted	$ 0.60	$ 0.59	$ 1.17	$ 0.64
Weighted-average anti-dilutive potential common shares	19,397	548,821	17,701	602,809