Earnings Per Share - Computation of basic and diluted EPS - (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Basic earnings per common share:
Net income	$ 42,326	$ 18,264
Weighted Average Number of Shares Outstanding, Basic	36,646	28,892
Basic earnings per common share (in dollars per share)	$ 1.15	$ 0.63
Diluted earnings per share:
Net income	$ 42,326	$ 18,264
Weighted Average Number of Shares Outstanding, Basic	36,646	28,892
Effect of dilutive securities (in shares)	253	267
Weighted-average dilutive shares	36,899	29,159
Diluted earnings per common share (in dollars per share)	$ 1.15	$ 0.63