Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Basic and Diluted Earnings per Share [Line Items]
Net income		$ 12,368	$ 19,534	$ 37,909	$ 58,231
Weighted-average common shares outstanding (in shares)		25,389,633	25,067,080	25,322,427	25,027,382
Weighted-average common shares for EPS calculation (in shares)		25,815,346	25,379,348	25,711,014	25,171,881
Basic earnings per common share (in dollars per share)		$ 0.49	$ 0.78	$ 1.50	$ 2.33
Diluted earnings per common share (in dollars per share)		$ 0.48	$ 0.77	$ 1.47	$ 2.31
Awards excluded from diluted earnings per share calculation (in shares)	[1]	0	260,035	0	410,425
Restricted Stock Unit Awards
Basic and Diluted Earnings per Share [Line Items]
Add dilutive effect of share-based awards outstanding (in shares)		155,270	125,135	155,270	125,135
Stock Options
Basic and Diluted Earnings per Share [Line Items]
Add dilutive effect of share-based awards outstanding (in shares)		270,443	187,133	233,317	19,364

[1] Outstanding awards that are not "in-the-money" are excluded from the diluted earnings per share calculation because the effect of including them would have been anti-dilutive.