Earnings per Share - Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 13,768	$ 15,786	$ 39,793	$ 44,033
Total Basic Weighted-Average Shares Outstanding (in shares)	[1]	17,851,780	17,489,380	18,000,234	17,752,788
Dilutive Effect of B Units (in shares)		52,130,690	51,930,114	52,124,914	51,537,499
Dilutive Effect of Options (in shares)		325,436	691,159	584,255	1,071,344
Dilutive Effect of Phantom Class B Units & Phantom Shares of Class A Common Stock (in shares)		3,226,094	1,461,725	3,196,468	1,463,747
Dilutive Effect of Restricted Shares of Class A Common Stock (in shares)		42,272	56,828	43,466	60,433
Diluted Weighted Average Common Shares Outstanding (in shares)		73,576,272	71,629,206	73,949,337	71,885,811
Participating Class B Units (in shares)		73,196	48,600	73,196	48,600
Diluted Weighted-Average Shares Outstanding (in shares)	[1]	73,649,468	71,677,806	74,022,533	71,934,411
Diluted Earnings per Share (in dollars per share)		$ 0.19	$ 0.22	$ 0.54	$ 0.61
Options to Purchase Class B Units
Diluted Net Income Allocated to:
Antidilutive securities excluded from diluted EPS (in shares)		300,000	400,000	300,000	400,000
Options to Purchase Shares of Class A Common Stock
Diluted Net Income Allocated to:
Antidilutive securities excluded from diluted EPS (in shares)		100,000	100,000	100,000	100,000
Contingent Options to Purchase Shares of Class A Common Stock
Diluted Net Income Allocated to:
Antidilutive securities excluded from diluted EPS (in shares)		2,000,000	2,000,000	2,000,000	2,000,000
Common Class A
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 13,754	$ 15,775	$ 39,752	$ 44,002
Total Basic Weighted-Average Shares Outstanding (in shares)		17,851,780	17,489,380	18,000,234	17,752,788
Participating Class B Units
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 14	$ 11	$ 41	$ 31

[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.