Earnings Per Share - Computation of basic and diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Basic earnings per common share:
Net income	$ 44,367	$ 42,326
Weighted-average basic common shares	35,445	36,646
Basic earnings per common share (in dollars per share)	$ 1.25	$ 1.15
Diluted earnings per share:
Net income	$ 44,367	$ 42,326
Weighted-average basic common shares	35,445	36,646
Effect of dilutive securities (in shares)	174	253
Weighted-average dilutive shares	35,619	36,899
Diluted earnings per common share (in dollars per share)	$ 1.25	$ 1.15