Earnings per Common Share - Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share, Basic and Diluted [Line Items]
Net income	$ 27,259	$ 25,193	$ 72,253	$ 70,871
Weighted average common shares outstanding for basic earnings per share computation	56,094,401	44,415,213	49,514,818	44,505,544
Dilutive effects of stock-based compensation	436,467	390,708	486,064	379,368
Weighted average common shares outstanding for diluted earnings per common share computation	56,530,868	44,805,921	50,000,882	44,884,912
Basic earnings per common share (in dollars per share)	$ 0.49	$ 0.57	$ 1.46	$ 1.59
Diluted earnings per common share (in dollars per share)	$ 0.48	$ 0.56	$ 1.45	$ 1.58
Unvested Restricted Stock
Earnings Per Share, Basic and Diluted [Line Items]
Anti-dilutive unvested time restricted stock	0	135	94,210	95,886
Restricted stock
Earnings Per Share, Basic and Diluted [Line Items]
Anti-dilutive unvested time restricted stock			174,696	218,556