Selected Quarterly Financial Data (Unaudited) Selected Quarterly Financial Data (Unaudited) (Quarterly Financial information - 2013) (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
Selected Quarterly Financial Data [Abstract]
Net revenues	$ 32,790	$ 30,845	$ 27,089	$ 27,104	$ 25,870	$ 23,396	$ 20,916	$ 23,135	$ 117,828	$ 93,317	$ 83,739
Investment and other gains	3,267	3	14	22	4,759	46	35	37
Income from continuing operations attributable to common stockholders	24,114	22,035	18,300	14,050	27,171	13,282	15,859	16,355	78,499	72,667	69,817
Discontinued operations	3,661	20,709	1,621	1,693	13,934	1,068	1,068	1,994
Net income attributable to common stockholders	$ 27,775	$ 42,744	$ 19,921	$ 15,743	$ 41,105	$ 14,350	$ 16,927	$ 18,349	$ 106,183	$ 90,731	$ 81,132
Weighted average common shares outstanding:
Basic	29,831,176	27,876,176	27,876,176	27,876,176	27,848,002	27,830,311	27,792,834	27,776,104	28,362,398	27,811,813	27,719,096
Diluted	29,860,614	27,905,545	27,913,727	27,911,584	27,868,245	27,862,582	27,820,831	27,803,222	28,397,702	27,838,720	27,792,592
Basic:
Income from continuing operations attributable to common stockholders	$ 0.81	$ 0.79	$ 0.65	$ 0.50	$ 0.98	$ 0.48	$ 0.57	$ 0.59	$ 2.77	$ 2.61	$ 2.52
Discontinued operations	$ 0.12	$ 0.74	$ 0.06	$ 0.06	$ 0.50	$ 0.04	$ 0.04	$ 0.07	$ 0.97	$ 0.65	$ 0.41
Net income per common share attributable to common stockholders	$ 0.93	$ 1.53	$ 0.71	$ 0.56	$ 1.48	$ 0.52	$ 0.61	$ 0.66	$ 3.74	$ 3.26	$ 2.93
Diluted:
Income from continuing operations attributable to common stockholders	$ 0.81	$ 0.79	$ 0.65	$ 0.50	$ 0.97	$ 0.48	$ 0.57	$ 0.59	$ 2.77	$ 2.61	$ 2.51
Discontinued operations	$ 0.12	$ 0.74	$ 0.06	$ 0.06	$ 0.50	$ 0.04	$ 0.04	$ 0.07	$ 0.97	$ 0.65	$ 0.41
Net income per common share attributable to common stockholders	$ 0.93	$ 1.53	$ 0.71	$ 0.56	$ 1.47	$ 0.52	$ 0.61	$ 0.66	$ 3.74	$ 3.26	$ 2.92