Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Basic and Diluted Earnings per Share [Line Items]
Net income	$ 11,725		$ 8,730		$ 49,614		$ 42,630
Weighted-average common shares outstanding (in shares)	25,359,196		25,423,191		25,301,432		25,468,293
Weighted-average common share for EPS calculation (in shares)	25,571,621		25,526,662		25,514,211		25,566,646
Basic earnings per common share (in dollars per share)	$ 0.46		$ 0.34		$ 1.96		$ 1.67
Diluted earnings per common share (in dollars per share)	$ 0.45		$ 0.34		$ 1.94		$ 1.67
Awards excluded from diluted EPS calculation (in shares)	646,226	[1]	719,563	[1]	661,826	[1]	1,098,292	[1]
Restricted Stock Awards [Member]
Basic and Diluted Earnings per Share [Line Items]
Add dilutive effect of share-based awards outstanding (in shares)	59,849		56,608		59,849		56,608
Options Awards [Member]
Basic and Diluted Earnings per Share [Line Items]
Add dilutive effect of share-based awards outstanding (in shares)	152,576		46,863		152,930		41,745

[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.