Net Income per Share of Common Stock (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
Numerators for earnings per share:
Net income that is available to common shareholders	$ 4,749	$ 14,861	$ 19,174	$ 5,359
Denominator for basic earnings per share:
Weighted average shares outstanding	21,492,625	20,896,291	21,300,212	20,834,742
Denominator for diluted earnings per share:
Effect of stock options and restricted stock units	730,697	464,195	629,200	432,535
Adjusted weighted average shares and assumed conversions	22,223,322	21,360,486	21,929,412	21,267,277
Basic earnings per share	$ 0.22	$ 0.71	$ 0.90	$ 0.26
Diluted earnings per share	$ 0.21	$ 0.70	$ 0.87	$ 0.25