Earnings per Share - Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 12,808	$ 14,226
Total Basic Weighted-Average Shares Outstanding (in shares)	[1]	18,278,773	18,015,368
Dilutive Effect of B Units (in shares)		52,117,775	51,032,975
Dilutive Effect of Options (in shares)		642,203	1,603,865
Dilutive Effect of Phantom Class B Units & Phantom Shares of Class A Common Stock (in shares)		3,102,053	1,517,654
Dilutive Effect of Restricted Shares of Class A Common Stock (in shares)		44,120	67,500
Diluted Weighted Average Common Shares Outstanding (in shares)		74,184,924	72,237,362
Participating Class B Units (in shares)		73,196	48,600
Diluted Weighted-Average Shares Outstanding (in shares)	[1]	74,258,120	72,285,962
Diluted Earnings per Share (in dollars per share)		$ 0.17	$ 0.20
Options to Purchase Class B Units
Diluted Net Income Allocated to:
Antidilutive securities excluded from diluted EPS (in shares)		300,000	300,000
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
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
Common Class A
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 12,795	$ 14,216
Total Basic Weighted-Average Shares Outstanding (in shares)		18,278,773	18,015,368
Participating Shares of Restricted Class A Common Stock
Diluted Net Income Allocated to:
Total Basic Weighted-Average Shares Outstanding (in shares)		0	0
Participating Class B Units
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 13	$ 10

[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.