Earnings Per Common Share - Computation of basic and diluted EPS - (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic earnings per common share:
Net income	$ 31,823	$ 24,516	$ 50,087	$ 49,010
Weighted Average Number of Shares Outstanding, Basic	29,095	23,995	28,985	23,977
Basic earnings per common share (in dollars per share)	$ 1.09	$ 1.02	$ 1.73	$ 2.04
Diluted earnings per share:
Net income	$ 31,823	$ 24,516	$ 50,087	$ 49,010
Weighted Average Number of Shares Outstanding, Basic	29,095	23,995	28,985	23,977
Effect of dilutive securities (in shares)	270	242	267	228
Weighted-average dilutive shares	29,365	24,237	29,252	24,205
Diluted earnings per common share (in dollars per share)	$ 1.08	$ 1.01	$ 1.71	$ 2.02