Stockholders' Equity - Other (Details) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) item $ / shares shares	Sep. 30, 2020 USD ($) item $ / shares shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) item $ / shares shares	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) $ / shares shares	May 16, 2016 shares
Stockholders' Equity
Shares available for issuance	1,200	1,200		1,200
Stock option and restricted stock
Stock-based compensation
Stock-based compensation expense (in dollars) | $		$ 1,300	$ 2,200	$ 4,000	$ 3,500
Stock options
Stock-based compensation
Unrecognized compensation cost related to unvested stock options (in dollars) | $	$ 2,800	$ 2,800		$ 2,800
Weighted-average periods over which unrecognized compensation cost recognized				1 year 6 months
Estimated forfeitures (as a percent)	1.50%	1.50%		1.50%
Valuation assumptions
Dividend yield (as a percent)				0.00%
Number of shares
Outstanding at the beginning of the period (in shares)				3,855
Granted (in shares)				25
Outstanding at the end of the period (in shares)	3,880	3,880		3,880		3,855
Vested at the end of the period (in shares)	3,102	3,102		3,102
Exercisable at the end of the period (in shares)	3,102	3,102		3,102
Weighted-average exercise price
Outstanding at the beginning of the period (in dollars per share) | $ / shares				$ 11.72
Granted (in dollars per share) | $ / shares				9.29
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 11.66	$ 11.66		11.66		$ 11.72
Vested at the end of the period (in dollars per share) | $ / shares	11.56	11.56		11.56
Exercisable at the end of the period (in dollars per share) | $ / shares	$ 11.56	$ 11.56		$ 11.56
Weighted-average remaining contractual term
Outstanding				5 years 3 months 18 days		6 years 1 month 6 days
Granted				6 years
Vested at the end of the period				4 years 4 months 24 days
Exercisable at the end of the period				4 years 4 months 24 days
Aggregate intrinsic value
Outstanding at the beginning of the period (in dollars) | $				$ 12,101
Outstanding at the end of the period (in dollars) | $						$ 12,101
Restricted Stock
Stock-based compensation
Unrecognized compensation cost related to unvested restricted stock (in dollars) | $	$ 3,800	$ 3,800		$ 3,800
Weighted-average periods over which unrecognized compensation cost recognized	1 year 4 months 24 days
Number of shares
Outstanding at the beginning of the period (in shares)				592
Granted (in shares)				118
Vested (in shares)				(237)
Outstanding at the end of the period (in shares)	473	473		473		592
Weighted-average grant date fair value
Outstanding at the beginning of the period (in dollars per share) | $ / shares				$ 12.32
Granted (in dollars per share) | $ / shares				9.29
Vested (in dollars per share) | $ / shares				12.75
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 11.34	$ 11.34		$ 11.34		$ 12.32
Time Based Restricted Stock Awards and Stock Option
Stockholders' Equity
Number of equal annual installments for vesting of awards | item	3	3		3
Time Based Stock Option | Black Scholes Pricing Model
Valuation assumptions
Risk-free interest rate (as a percent)				0.40%		1.60%
Volatility (as a percent)				44.20%		40.30%
Weighted-average expected term (years)				6 years		6 years
Time Based Restricted Stock
Aggregate intrinsic value
Vesting period				3 years
Common Class A
Stockholders' Equity
Shares authorized for issuance							7,200