Earnings per Share - Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 12,374	$ 13,768	$ 23,119	$ 39,793
Total Basic Weighted-Average Shares Outstanding (in shares)	[1]	16,931,447	17,851,780	17,310,875	18,000,234
Dilutive Effect of B Units (in shares)		54,264,501	52,130,690	54,119,584	52,124,914
Dilutive Effect of Options (in shares)		5,418	325,436	10,658	584,255
Dilutive Effect of Phantom Class B Units & Phantom Shares of Class A Common Stock (in shares)		1,747,495	3,226,094	1,735,983	3,196,468
Dilutive Effect of Restricted Shares of Class A Common Stock (in shares)		10,236	42,272	9,735	43,466
Diluted Weighted Average Common Shares Outstanding (in shares)		72,959,097	73,576,272	73,186,835	73,949,337
Participating Class B Units and Class B-1 Units (in shares)		5,824,112	73,196	5,897,774	73,196
Diluted Weighted-Average Shares Outstanding (in shares)	[1]	78,783,209	73,649,468	79,084,609	74,022,533
Diluted Earnings per Share (in dollars per share)	[2]	$ 0.16	$ 0.19	$ 0.28	$ 0.54
Options to Purchase Class B Units
Diluted Net Income Allocated to:
Antidilutive securities excluded from diluted EPS (in shares)		5.5	0.3	5.5	0.3
Options to Purchase Shares of Class A Common Stock
Diluted Net Income Allocated to:
Antidilutive securities excluded from diluted EPS (in shares)		0.2	0.1	0.2	0.1
Contingent Options to Purchase Shares of Class A Common Stock
Diluted Net Income Allocated to:
Antidilutive securities excluded from diluted EPS (in shares)		1.0	2.0	1.0	2.0
Common Class A
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 11,435	$ 13,754	$ 21,353	$ 39,752
Total Basic Weighted-Average Shares Outstanding (in shares)		16,914,641	17,851,780	17,301,491	18,000,234
Participating Shares of Restricted Class A Common Stock
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 3		$ 3
Total Basic Weighted-Average Shares Outstanding (in shares)	[3]	16,806		9,384
Participating Class B Units
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 936	$ 14	$ 1,763	$ 41

[1] ^{The Company issues restricted shares of Class A common stock and restricted Class B units that have non-forfeitable dividend rights.  Under the "two-class method," these shares and units are considered participating securities and are required to be included in the computation of basic and diluted earnings per share.}

[2] ^{During the nine months ended September 30, 2020, the calculation of diluted earnings per share resulted in an increase in earnings per share. Therefore, diluted earnings per share is assumed to be equal to basic earnings per share. Please refer to Note 5, “Earnings per Share,” for further details.}

[3] Certain unvested shares of Class A common stock granted to employees have nonforfeitable rights to dividends and therefore participate fully in the results of the Company from the date they are granted. They are included in the computation of basic earnings per share using the two-class method for participating securities.