Net Income Per Share (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Income Per Share [Abstract]
Common shares									24,850,830	25,890,521	29,140,879
Vested restricted stock units									558,825	411,768	252,430
Weighted Average Number of Shares Outstanding, Basic, Total	24,756,286	24,908,247	25,925,627	26,157,672	26,021,682	26,032,983	25,974,772	27,195,580	25,409,655	26,302,289	29,393,309
Dilutive effect of stock options									48,005	102,651	335,389
Dilutive effect of restricted stock and restricted stock units									141,296	195,915	256,121
Dilutive number of weighted average shares outstanding	24,926,004	24,962,054	25,979,872	26,283,801	26,258,668	26,135,755	26,110,528	27,489,326	25,598,956	26,600,855	29,984,819
Restricted stock outstanding excluded from calculation of diluted net income per share									0	0