UNAUDITED CONSOLIDATED STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Common Class A	Common Class B	Additional Paid-In Capital	Accumulated Other Comprehensive (Loss)/ Income	Retained Earnings	Non-Controlling Interests
Beginning Balance at Dec. 31, 2017	$ 99,289	$ 180		$ 7,915	$ (5)	$ 24,214	$ 66,985
Beginning Balance (in shares) at Dec. 31, 2017		18,096,554	50,709,673
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			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 Adjustments	68				(18)		86
Repurchase and Retirement of Class A Common Stock	(3,203)	$ (3)		(3,200)
Repurchase and Retirement Shares/Units (in shares)		(293,130)	(3,870)
Repurchase and Retirement of Class B Units	(41)			(11)			(30)
Class A Cash Dividends Declared and Paid	(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
Beginning Balance at Dec. 31, 2017	99,289	$ 180		7,915	(5)	24,214	66,985
Beginning Balance (in shares) at Dec. 31, 2017		18,096,554	50,709,673
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Sale of Shares under Equity Incentive Plan (in shares)			897,515
Net Income	$ 54,470
Options Exercised (in shares)	0
Repurchase and Retirement Shares/Units (in shares)		(742,255)	(3,870)
Ending Balance at Sep. 30, 2018	$ 97,453	$ 173		2,372	18	26,854	68,036
Ending Balance (in shares) at Sep. 30, 2018		17,364,299	51,930,427
Beginning Balance at Mar. 31, 2018	82,200	$ 177		5,800	(23)	20,177	56,069
Beginning Balance (in shares) at Mar. 31, 2018		17,813,424	51,033,459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Amortization of Non-Cash Compensation	1,221			312			909
Sale of Shares under Equity Incentive Plan	5,184			1,340			3,844
Sale of Shares under Equity Incentive Plan (in shares)			896,489
Directors' Share Grants	102			26			76
Net Income	17,357					3,472	13,885
Foreign Currency Translation Adjustments	(131)				34		(165)
Repurchase and Retirement of Class A Common Stock	(2,279)	$ (2)		(2,277)
Repurchase and Retirement Shares/Units (in shares)		(232,340)
Class A Cash Dividends Declared and Paid	(532)					(532)
Contributions to Non-Controlling Interests	31						31
Distributions to Non-Controlling Interests	(10,798)						(10,798)
Other				(528)			528
Ending Balance at Jun. 30, 2018	92,355	$ 175		4,673	11	23,117	64,379
Ending Balance (in shares) at Jun. 30, 2018		17,581,084	51,929,948
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Amortization of Non-Cash Compensation	1,240			312			928
Sale of Shares under Equity Incentive Plan	3			1			2
Sale of Shares under Equity Incentive Plan (in shares)			479
Directors' Share Grants	102			26			76
Net Income	19,447					4,262	15,185
Foreign Currency Translation Adjustments	$ (27)				7		(34)
Options Exercised (in shares)	0
Repurchase and Retirement of Class A Common Stock	$ (2,019)	$ (2)		(2,017)
Repurchase and Retirement Shares/Units (in shares)		(216,785)
Class A Cash Dividends Declared and Paid	(525)					(525)
Tax Impact of Transactions with Non-Controlling Shareholders	(420)			(420)
Contributions to Non-Controlling Interests	30						30
Distributions to Non-Controlling Interests	(12,733)						(12,733)
Other				(203)			203
Ending Balance at Sep. 30, 2018	97,453	$ 173		2,372	18	26,854	68,036
Ending Balance (in shares) at Sep. 30, 2018		17,364,299	51,930,427
Beginning Balance at Dec. 31, 2018	99,008	$ 183		3,913	35	28,871	66,006
Beginning Balance (in shares) at Dec. 31, 2018		18,398,211	51,253,526
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Amortization of Non-Cash Compensation	1,554			414			1,140
Amortization of Non-Cash Compensation (in shares)		10,000	241,996
Issuance of Shares under Equity Incentive Plan	4,087			1,065			3,022
Issuance of Shares under Equity Incentive Plan (in shares)			715,874
Sale of Shares under Equity Incentive Plan	65			17			48
Sale of Shares under Equity Incentive Plan (in shares)			10,399
Directors' Share Grants	301			78			223
Net Income	15,942					3,102	12,840
Foreign Currency Translation Adjustments	63				(17)		80
Repurchase and Retirement of Class A Common Stock	(4,712)	$ (5)		(4,369)		(338)
Repurchase and Retirement Shares/Units (in shares)		(533,369)	(95,739)
Repurchase and Retirement of Class B Units	(675)			(176)			(499)
Class A Cash Dividends Declared and Paid	(8,951)					(8,951)
Tax Impact of Transactions with Non-Controlling Shareholders	(207)			(207)
Contributions from Non-Controlling Interests	23						23
Distributions to Non-Controlling Interests	(25,665)						(25,665)
Other				(735)			735
Ending Balance at Mar. 31, 2019	80,833	$ 178			18	22,684	57,953
Ending Balance (in shares) at Mar. 31, 2019		17,874,842	52,126,056
Beginning Balance at Dec. 31, 2018	99,008	$ 183		3,913	35	28,871	66,006
Beginning Balance (in shares) at Dec. 31, 2018		18,398,211	51,253,526
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Sale of Shares under Equity Incentive Plan (in shares)			16,137
Net Income	$ 49,153
Options Exercised (in shares)	483,000	59,875
Repurchase and Retirement Shares/Units (in shares)		(709,466)	(109,357)
Ending Balance at Sep. 30, 2019	$ 95,650	$ 176		59	63	28,454	66,898
Ending Balance (in shares) at Sep. 30, 2019		17,758,620	52,146,946
Beginning Balance at Mar. 31, 2019	80,833	$ 178			18	22,684	57,953
Beginning Balance (in shares) at Mar. 31, 2019		17,874,842	52,126,056
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Amortization of Non-Cash Compensation	1,666			425			1,241
Sale of Shares under Equity Incentive Plan	1						1
Sale of Shares under Equity Incentive Plan (in shares)			237
Directors' Share Grants	103			26			77
Net Income	16,295					3,364	12,931
Foreign Currency Translation Adjustments	(73)				19		(92)
Class A Cash Dividends Declared and Paid	(536)					(536)
Tax Impact of Transactions with Non-Controlling Shareholders	(110)			(110)
Contributions from Non-Controlling Interests	5						5
Distributions to Non-Controlling Interests	(6,972)						(6,972)
Other				(52)			52
Ending Balance at Jun. 30, 2019	91,212	$ 178		289	37	25,512	65,196
Ending Balance (in shares) at Jun. 30, 2019		17,874,842	52,126,293
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Amortization of Non-Cash Compensation	1,666			425			1,241
Sale of Shares under Equity Incentive Plan	31			8			23
Sale of Shares under Equity Incentive Plan (in shares)			5,501
Directors' Share Grants	104			27			77
Net Income	16,916					3,478	13,438
Foreign Currency Translation Adjustments	$ (104)				26		(130)
Options Exercised (in shares)	483,000	59,875	28,770
Repurchase and Retirement of Class A Common Stock	$ (1,486)	$ (2)		(377)			(1,107)
Repurchase and Retirement Shares/Units (in shares)		(176,097)	(13,618)
Repurchase and Retirement of Class B Units	(134)			(35)			(99)
Class A Cash Dividends Declared and Paid	(536)					(536)
Tax Impact of Transactions with Non-Controlling Shareholders	(120)			(120)
Contributions from Non-Controlling Interests	56						56
Distributions to Non-Controlling Interests	(11,955)						(11,955)
Other				(158)			158
Ending Balance at Sep. 30, 2019	$ 95,650	$ 176		$ 59	$ 63	$ 28,454	$ 66,898
Ending Balance (in shares) at Sep. 30, 2019		17,758,620	52,146,946