Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 2,729	$ 2,019	$ 43,039	$ 38,660
Average common shares outstanding - basic (in shares)	28,648	27,510	28,641	27,479
Additional shares for stock-based compensation plans (in shares)	69	122	81	112
Average common shares outstanding - diluted (in shares)	28,717	27,632	28,722	27,591
Earnings per share of common stock - basic (in dollars per share)	$ 0.10	$ 0.07	$ 1.50	$ 1.41
Earnings per share of common stock - diluted (in dollars per share)	$ 0.10	$ 0.07	$ 1.50	$ 1.40
Antidilutive shares (in shares)	32	23	21	16