Selected Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
SELECTED QUARTERLY FINANCIAL DATA [Abstract]
Net Revenues	$ 21,524	$ 20,454	$ 20,199	$ 20,525	$ 19,510	$ 19,419	$ 19,011	$ 20,092	$ 82,702	$ 78,032	$ 62,793
Investment income and other	1,346	2,196	9,790	1,412	1,232	1,241	1,285	1,433	14,744	5,191	8,581
Income from continuing operations	16,904	16,525	23,841	15,490	15,583	15,963	15,868	14,425	72,760	61,840	57,061
Income from discontinued operations	1,210	2,283	1,276	3,603	1,371	1,371	3,321	1,519	8,372	7,581	7,168
Net income	$ 18,114	$ 18,808	$ 25,117	$ 19,093	$ 16,954	$ 17,334	$ 19,189	$ 15,944	$ 81,132	$ 69,421	$ 64,229
Weighted average common shares outstanding:
Basic	27,741,961	27,729,560	27,708,136	27,696,727	27,686,217	27,673,703	27,665,629	27,632,376	27,719,096	27,664,482	27,586,338
Diluted	27,784,915	27,789,725	27,799,616	27,796,109	27,783,517	27,737,802	27,729,034	27,681,479	27,792,592	27,732,959	27,618,300
Earnings per common share, Basic:
Income from continuing operations	$ 0.61	$ 0.60	$ 0.86	$ 0.56	$ 0.56	$ 0.57	$ 0.57	$ 0.52	$ 2.63	$ 2.24	$ 2.07
Discontinued operations	$ 0.04	$ 0.08	$ 0.05	$ 0.13	$ 0.05	$ 0.05	$ 0.12	$ 0.06	$ 0.30	$ 0.27	$ 0.26
Net income per common share	$ 0.65	$ 0.68	$ 0.91	$ 0.69	$ 0.61	$ 0.62	$ 0.69	$ 0.58	$ 2.93	$ 2.51	$ 2.33
Earnings per common share, Diluted:
Income from continuing operations	$ 0.61	$ 0.60	$ 0.85	$ 0.56	$ 0.56	$ 0.57	$ 0.57	$ 0.52	$ 2.62	$ 2.23	$ 2.06
Discontinued operations	$ 0.04	$ 0.08	$ 0.05	$ 0.13	$ 0.05	$ 0.05	$ 0.12	$ 0.06	$ 0.30	$ 0.27	$ 0.26
Net income per common share	$ 0.65	$ 0.68	$ 0.90	$ 0.69	$ 0.61	$ 0.62	$ 0.69	$ 0.58	$ 2.92	$ 2.50	$ 2.32