Net Income Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Computation of basic and diluted net income per common share
Net income	$ 12,965	$ 34,122
Net income per common share - basic (in dollars per share)	$ 0.27	$ 0.73
Net income per common share - diluted (in dollars per share)	$ 0.27	$ 0.71
Weighted average common shares outstanding - basic (in shares)	47,359	46,784
Plus dilutive effect of potential common shares (in shares)	282	988
Weighted average common shares outstanding - diluted (in shares)	47,641	47,772
Common stock excluded from calculation of EPS (in shares)	27	66