Earnings per Share - Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 14,226	$ 8,704
Total Basic Weighted-Average Shares Outstanding (in shares)	[1]	18,015,368	17,361,153
Dilutive Effect of B Units (in shares)		51,032,975	51,097,254
Dilutive Effect of Options (in shares)		1,603,865	508,963
Dilutive Effect of Phantom Class B Units & Phantom Shares of Class A Common Stock (in shares)		1,517,654	1,791,662
Dilutive Effect of Restricted Shares of Class A Common Stock (in shares)		67,500	70,780
Diluted Weighted Average Common Shares Outstanding (in shares)		72,237,362	70,829,812
Participating Class B Units (in shares)		48,600	64,886
Diluted Weighted-Average Shares Outstanding (in shares)	[1]	72,285,962	70,894,698
Diluted Earnings per Share (in dollars per share)		$ 0.20	$ 0.12
Options to Purchase Class B Units
Diluted Net Income Allocated to:
Antidilutive securities excluded from diluted EPS (in shares)		300,000	700,000
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	3,000,000
Common Class A
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 14,216	$ 8,694
Total Basic Weighted-Average Shares Outstanding (in shares)		18,015,368	17,350,367
Participating Shares of Restricted Class A Common Stock
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 0	$ 2
Total Basic Weighted-Average Shares Outstanding (in shares)		0	10,786
Participating Class B Units
Diluted Net Income Allocated to:
Total Diluted Net Income Attributable to Shareholders		$ 10	$ 8

[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.