Selected Quarterly Financial Data (Unaudited) Selected Quarterly Financial Data (Unaudited) (Quarterly Financial information - 2015) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Selected Quarterly Financial Data [Abstract]
Net revenues	$ 58,642	$ 58,282	$ 56,313	$ 55,751	$ 45,735	$ 44,478	$ 44,160	$ 43,136	$ 228,988	$ 177,509	$ 117,828
Investment and other gains	23,529	1,126	0	0
Income from continuing operations attributable to common stockholders	54,397	33,600	31,182	29,683					148,862	101,609	78,499
Net income attributable to common stockholders	$ 54,397	$ 33,600	$ 31,182	$ 29,683	$ 27,532	$ 25,250	$ 25,294	$ 23,533	$ 148,862	$ 101,609	$ 106,183
Weighted average common shares outstanding:
Basic	37,727,868	37,566,221	37,566,221	37,558,067	34,343,706	33,055,992	33,052,750	33,051,415	37,604,594	33,375,966	28,362,398
Diluted	37,741,162	37,583,141	37,607,117	37,645,265	34,402,969	33,088,570	33,087,283	33,085,232	37,644,171	33,416,014	28,397,702
Basic:
Net income per common share attributable to common stockholders	$ 1.44	$ 0.89	$ 0.83	$ 0.79	$ 0.80	$ 0.76	$ 0.77	$ 0.71	$ 3.96	$ 3.04	$ 3.74
Diluted:
Net income per common share attributable to common stockholders	$ 1.44	$ 0.89	$ 0.83	$ 0.79	$ 0.80	$ 0.76	$ 0.76	$ 0.71	$ 3.95	$ 3.04	$ 3.74