Earnings Per Share - Computation of basic and diluted EPS - (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic earnings per common share:
Net income	$ 47,082	$ 35,046	$ 129,867	$ 85,133
Weighted Average Number of Shares Outstanding, Basic	36,645	29,115	36,657	29,023
Basic earnings per common share (in dollars per share)	$ 1.28	$ 1.20	$ 3.53	$ 2.92
Diluted earnings per share:
Net income	$ 47,082	$ 35,046	$ 129,867	$ 85,133
Weighted Average Number of Shares Outstanding, Basic	36,645	29,115	36,657	29,023
Effect of dilutive securities (in shares)	248	270	252	268
Weighted-average dilutive shares	36,893	29,385	36,909	29,291
Diluted earnings per common share (in dollars per share)	$ 1.28	$ 1.19	$ 3.52	$ 2.90