UNAUDITED CONSOLIDATED STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Common Class A	Common Class B	Common Stock Common Class A	Common Stock Common Class B	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Retained Earnings	Non-Controlling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustment for the Cumulative Effect of Applying ASU 2016-09	$ 1,377							$ 1,377	$ 0
Adjusted Balance	82,711			$ 173		$ 5,996	$ (25)	23,726	52,841
Beginning Balance (in shares) at Dec. 31, 2016				17,340,090	50,461,598
Beginning Balance at Dec. 31, 2016	81,334			$ 173		5,996	(25)	22,349	52,841
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Amortization of Non-Cash Compensation	1,160					300			860
Amortization of Non-Cash Compensation (in shares)				24,934	16,671
Issuance of Shares under Equity Incentive Plan	4,413					1,118			3,295
Issuance of Shares under Equity Incentive Plan (in shares)					620,543
Sale of Shares under Equity Incentive Plan	25				$ 100	6			19
Sale of Shares under Equity Incentive Plan (in shares)					3,888
Directors' Share Grants	181					46			135
Net Income	12,726							2,336	10,390
Foreign Currency Translation Adjustment	12						3		9
Repurchase and Retirement of Class A Common Stock	(77)			$ 0		(77)
Repurchase and Retirement of Class B Units	(39)					(10)			(29)
Repurchase and Retirement Shares/Units (in shares)				(8,416)	(2,897)
Class A Cash Dividends Declared and Paid ($0.42 and $0.28 per share for three months ended March 31, 2018 and 2017)	(4,862)							(4,862)
Contributions from Non-Controlling Interests	2,427								2,427
Distributions to Non-Controlling Interests	(19,750)								(19,750)
Other						(233)			233
Ending Balance at Mar. 31, 2017	78,927			$ 173		7,146	(22)	21,200	50,430
Ending Balance (in shares) at Mar. 31, 2017				17,356,608	51,099,803
Beginning Balance (in shares) at Dec. 31, 2017		18,096,554	50,709,673	18,096,554	50,709,673
Beginning Balance at Dec. 31, 2017	99,289			$ 180		7,915	(5)	24,214	66,985
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Amortization of Non-Cash Compensation	1,260					339			921
Amortization of Non-Cash Compensation (in shares)				10,000	26,178
Issuance of Shares under Equity Incentive Plan	4,191					1,096			3,095
Issuance of Shares under Equity Incentive Plan (in shares)					300,931
Sale of Shares under Equity Incentive Plan	4				$ 100	1			3
Sale of Shares under Equity Incentive Plan (in shares)					547
Directors' Share Grants	245					64			181
Net Income	17,666							3,523	14,143
Foreign Currency Translation Adjustment	68						(18)		86
Repurchase and Retirement of Class A Common Stock	(3,203)			$ (3)		(3,200)
Repurchase and Retirement of Class B Units	(41)					(11)			(30)
Repurchase and Retirement Shares/Units (in shares)				(293,130)	(3,870)
Class A Cash Dividends Declared and Paid ($0.42 and $0.28 per share for three months ended March 31, 2018 and 2017)	(7,560)							(7,560)
Distributions to Non-Controlling Interests	(29,719)								(29,719)
Other						(404)			404
Ending Balance at Mar. 31, 2018	$ 82,200			$ 177		$ 5,800	$ (23)	$ 20,177	$ 56,069
Ending Balance (in shares) at Mar. 31, 2018		17,813,424	51,033,459	17,813,424	51,033,459