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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings per Share [Abstract]
Net income available to common stockholders - basic	$ 5,730	$ 7,009	$ 16,719	$ 15,723
Effect of net income attributable to noncontrolling interests	808	1,229	2,485	3,072
Net income available to common stockholders - diluted	$ 6,538	$ 8,238	$ 19,204	$ 18,795
Weighted average shares outstanding-basic	47,854,516	40,994,387	45,651,421	36,354,738
Effect of Class A and Class RS partnership units	6,767,000	6,932,000	6,787,000	7,103,000
Effect of Class O units and options to purchase Class A common stock on an "as if" converted basis	1,066,000	807,000	982,000	724,000
Weighted average shares outstanding-diluted	55,687,665	48,733,417	53,420,326	44,181,583
Net income per share attributable to common stockholders - basic	$ 0.12	$ 0.17	$ 0.37	$ 0.43
Net income per share attributable to common stockholders - diluted	$ 0.12	$ 0.17	$ 0.36	$ 0.43