Net Income Per Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013		Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income	$ 8,164	$ 8,385	$ 1,891	$ 9,564	$ 5,289	[1]	$ 10,082	$ 3,488	[2]	$ 13,173	$ 28,004	$ 32,032	$ 40,402
Less distributed and undistributed earnings allocated to participating securities											(2,002)	(916)	(1,224)
Net income allocated to common shares											$ 26,002	$ 31,116	$ 39,178
Weighted average common shares outstanding											24,708	24,850	25,007
Incremental shares from assumed conversions of common stock options											4	22	60
Adjusted weighted average common shares outstanding											24,712	24,872	25,067
Potentially dilutive securities not included in weighted average share calculation due to anti-dilutive effect											4	8	29

[1] Includes a $2.0 million tax benefit related to tax years 2009 through 2012. Please read Note 9 to the Consolidated Financial Statements, “Income Taxes,” for additional information.

[2] Includes a non-cash impairment charge in the second quarter of 2013 of $2.7 million. Please read Note 6 to the Consolidated Financial Statements, “Other Assets,” for additional information.