Earnings Per Common Share - Computation of basic and diluted EPS - (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Basic earnings per common share:
Net income	$ 18,264	$ 24,494
Weighted Average Number of Shares Outstanding, Basic	28,892	23,969
Basic earnings per common share (in dollars per share)	$ 0.63	$ 1.02
Diluted earnings per share:
Net income	$ 18,264	$ 24,494
Weighted Average Number of Shares Outstanding, Basic	28,892	23,969
Effect of dilutive securities (in shares)	267	222
Weighted-average dilutive shares	29,159	24,191
Diluted earnings per common share (in dollars per share)	$ 0.63	$ 1.01