Earnings Per Share Earnings Per Share - Reconciliation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share [Abstract]
Numerator for basic and diluted EPS — net income allocated to common stockholders	$ 15,800	$ 1,800	$ 15,500	$ 13,600	$ 15,100	$ 8,600	$ 2,200	$ 16,100	$ 46,682	$ 42,092	$ 44,578
Denominator for basic EPS — weighted average number of shares (shares)									30,134,430	30,553,460	31,020,894
Add — dilutive effect of:
Weighted average number of incremental shares issuable from restricted stock units (shares)									27,000	8,000	14,000
Denominator for diluted EPS — weighted average number of shares and dilutive potential shares (shares)									30,160,669	30,561,682	31,034,817
Earnings per share:
Basic (usd per share)	$ 0.53	$ 0.06	$ 0.52	$ 0.45	$ 0.50	$ 0.28	$ 0.07	$ 0.53	$ 1.55	$ 1.38	$ 1.44
Diluted (usd per share)	$ 0.53	$ 0.06	$ 0.52	$ 0.45	$ 0.50	$ 0.28	$ 0.07	$ 0.53	$ 1.55	$ 1.38	$ 1.44