Earnings per Share (Reconciliation between Basic and Diluted Earnings per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income for basic and diluted earnings per share	$ 20,509	$ 29,242	$ 29,242	$ 75,070	$ 84,630
Basic weighted average shares outstanding	30,501	31,492		30,517	31,480
Dilutive effect of stock options and restricted stock awards	132	136		81	158
Diluted weighted average shares outstanding	30,633	31,628		30,598	31,638
Basic earnings per common share	$ 0.67	$ 0.93		$ 2.46	$ 2.69
Diluted earnings per common share	$ 0.67	$ 0.92		$ 2.45	$ 2.67