Earnings per Share (Computation of Basic and Diluted Net Income per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings per Share [Abstract]
Net income available to common stockholders - basic	$ 7,009	$ 3,157	$ 15,723	$ 10,445
Effect of net income attributable to noncontrolling interests	1,229	849	3,072	2,810
Net income available to common stockholders - diluted	$ 8,238	$ 4,006	$ 18,795	$ 13,255
Weighted average shares outstanding-basic	40,994,387	29,016,774	36,354,738	29,006,620
Effect of Class A and Class RS partnership units *	6,932,000	7,797,000	7,103,000	7,797,000
Effect of Class O units and options to purchase Class A common stock on an "as if" converted basis	807,000	438,000	724,000	236,000
Weighted average shares outstanding-diluted	48,733,417	37,251,769	44,181,583	37,039,603
Net income per share-basic	$ 0.17	$ 0.11	$ 0.43	$ 0.36
Net income per share-diluted	$ 0.17	$ 0.11	$ 0.43	$ 0.36