Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Basic and Diluted Earnings per Share [Line Items]
Net income	$ 10,685		$ 15,496		$ 24,016		$ 37,889
Weighted-average common shares outstanding (in shares)	25,330,066		25,297,718		25,351,056		25,271,752
Weighted-average common share for EPS calculation (in shares)	25,556,627		25,472,302		25,591,258		25,414,392
Basic earnings per common share (in dollars per share)	$ 0.42		$ 0.61		$ 0.95		$ 1.50
Diluted earnings per common share (in dollars per share)	$ 0.42		$ 0.61		$ 0.94		$ 1.49
Awards excluded from diluted earnings per share calculation(1)	904,580	[1]	647,726	[1]	904,580	[1]	663,326	[1]
Restricted Stock Awards [Member]
Basic and Diluted Earnings per Share [Line Items]
Add dilutive effect of share-based awards outstanding (in shares)	114,313		59,849		114,313		59,849
Stock Options [Member]
Basic and Diluted Earnings per Share [Line Items]
Add dilutive effect of share-based awards outstanding (in shares)	112,248		114,735		125,889		82,791

[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.