Stockholders' Equity - Warrants Issued to USAA and Third Party Marketing Firm (Details) $ / shares in Units, $ in Thousands					1 Months Ended		12 Months Ended
	May 01, 2014 tranche $ / shares shares	Jan. 01, 2012 $ / shares shares	Feb. 25, 2011 $ / shares shares	Jun. 25, 2010 $ / shares shares	Mar. 31, 2015 shares	May 31, 2014 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2011 shares	Nov. 24, 2009 $ / shares shares
Convertible Preferred Stock and Stockholders' Equity
Warrant expense | $							$ 46	$ (803)	$ 9,861
Proceeds from exercise of warrants | $							$ 0	0	$ 9,461
Common Stock Purchase Warrants | Third Party Marketing Firm
Convertible Preferred Stock and Stockholders' Equity
Exercise price of warrants (in dollars per share) | $ / shares			$ 6.02
Maximum number of shares under warrant agreement			1,433,333		1,433,333
Period of warrant			8 years
Number of shares under warrants that have been earned									343,665
Shares issued for exercise of warrants					959,676
Common Stock Purchase Warrants | Third Party Marketing Firm | Selling and Marketing Expense
Convertible Preferred Stock and Stockholders' Equity
Warrant expense | $									$ 2,300
Common Stock Purchase Warrants | Third Party Marketing Firm | Minimum
Convertible Preferred Stock and Stockholders' Equity
Expected life									4 years 9 months 18 days
Risk-free interest rate									1.51%
Volatility (as a percent)									46.60%
Common Stock Purchase Warrants | Third Party Marketing Firm | Maximum
Convertible Preferred Stock and Stockholders' Equity
Expected life									5 years 1 month 6 days
Risk-free interest rate									1.70%
Volatility (as a percent)									48.10%
USAA
Convertible Preferred Stock and Stockholders' Equity
Warrants earned and outstanding (in shares)							509,642
Remaining warrants available for issuance (in shares)							949,337
USAA | Common Stock Purchase Warrants
Convertible Preferred Stock and Stockholders' Equity
Warrant expense | $							$ 100	$ 200	$ 5,700
Number of shares under warrants that have been earned							10,666	71,330	631,449
Shares issued for exercise of warrants						3,265,168
Proceeds from exercise of warrants | $						$ 9,500
USAA | Common Stock Purchase Warrants | Warrant Agreement In March 2009
Convertible Preferred Stock and Stockholders' Equity
Shares that may be purchased under warrant											961,482
Exercise price of warrants (in dollars per share) | $ / shares											$ 0.83
USAA | Common Stock Purchase Warrants | Warrants Agreement in June 2010
Convertible Preferred Stock and Stockholders' Equity
Shares that may be purchased under warrant										1,653,333
Exercise price of warrants (in dollars per share) | $ / shares				$ 2.12
Maximum number of shares under warrant agreement				1,653,333
USAA | Common Stock Purchase Warrants | Warrants Agreement in January 2012
Convertible Preferred Stock and Stockholders' Equity
Exercise price of warrants (in dollars per share) | $ / shares		$ 7.95
Maximum number of shares under warrant agreement		1,042,666
Period of warrant		8 years
Period of warrant after expiration of the affinity agreement		90 days
USAA | 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
USAA | Common Stock Purchase Warrants | Affinity Group Marketing Agreement | Tranche One
Convertible Preferred Stock and Stockholders' Equity
Exercise price of warrants (in dollars per share) | $ / shares	$ 7.95
Maximum number of shares under warrant agreement	392,313
USAA | Common Stock Purchase Warrants | Affinity Group Marketing Agreement | Tranche Two
Convertible Preferred Stock and Stockholders' Equity
Exercise price of warrants (in dollars per share) | $ / shares	$ 15.00
Maximum number of shares under warrant agreement	1,066,666