Shareholders' Equity (Details)	3 Months Ended					9 Months Ended
	Sep. 30, 2020 vote $ / shares shares	Jun. 30, 2020 shares	Mar. 31, 2020 shares	Sep. 30, 2019 shares	Mar. 31, 2019 shares	Sep. 30, 2020 vote $ / shares shares	Sep. 30, 2019 $ / shares shares	Dec. 31, 2019 $ / shares	Apr. 19, 2018 USD ($)	Feb. 11, 2014 USD ($)	Apr. 24, 2012 USD ($)
Class of Stock [Line Items]
Amount authorized under stock repurchase program | $									$ 30,000,000	$ 20,000,000	$ 10,000,000
Common Class A
Class of Stock [Line Items]
Economic interest held in company by class of stock (in hundredths)	23.70%					23.70%		25.40%
Percentage of right to future income and distributions	21.90%					21.90%		24.10%
Par value (in dollars per share)	$ 0.01					$ 0.01		$ 0.01
Percentage of outstanding shares that represents rights of holders to receive distribution (in hundredths)	100.00%					100.00%
Common stock purchased and retired (in shares) | shares	102,015	266,238	823,792	176,097	533,369	1,192,045	709,466
Purchased under repurchase authorization at an average price per share (in dollars per share)						$ 6.34	$ 8.74
Common Class B
Class of Stock [Line Items]
Percentage of right to future income and distributions	70.60%					70.60%		71.00%
Par value (in dollars per share)	$ 0.000001					$ 0.000001		$ 0.000001
Voting rights (in votes) | vote						5
Percentage of stock holding that will entitle holders to one vote (in hundredths)						20.00%
Voting rights when class of stock constitutes less than 20% of all shares outstanding (in votes) | vote	1					1
Common stock purchased and retired (in shares) | shares			94,830	13,618	95,739	94,830	109,357
Purchased under repurchase authorization at an average price per share (in dollars per share)						$ 5.97	$ 6.48
Class B-1 Units
Class of Stock [Line Items]
Percentage of right to future income and distributions	7.50%					7.50%		4.90%
Voting rights (in votes) | vote						0
Number of shares issued | shares	0					0
Pzena Investment Management, LLC | Common Class B
Class of Stock [Line Items]
Economic interest held in company by class of stock (in hundredths)	76.30%					76.30%		74.60%