Stockholders' Equity - Warrants Issued to USAA and Third Party Marketing Firm (Details) - USAA		12 Months Ended
	May 01, 2014 tranche $ / shares shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Convertible Preferred Stock and Stockholders' Equity
Warrants earned and outstanding (in shares)		509,642
Remaining warrants available for issuance (in shares)		949,337
Common Stock Purchase Warrants
Convertible Preferred Stock and Stockholders' Equity
Warrant expense | $		$ 0	$ 0	$ 0
Common Stock Purchase Warrants | Affinity Group Marketing Agreement
Convertible Preferred Stock and Stockholders' Equity
Maximum number of shares under warrant agreement	1,458,979
Number of warrant tranches | tranche	2
Common Stock Purchase Warrants | Affinity Group Marketing Agreement | Tranche One
Convertible Preferred Stock and Stockholders' Equity
Maximum number of shares under warrant agreement	392,313
Exercise price of warrants (in dollars per share) | $ / shares	$ 7.95
Common Stock Purchase Warrants | Affinity Group Marketing Agreement | Tranche Two
Convertible Preferred Stock and Stockholders' Equity
Maximum number of shares under warrant agreement	1,066,666
Exercise price of warrants (in dollars per share) | $ / shares	$ 15.00