Stockholders' Equity - Employee Stock Purchase Plan (Details) - Employee Stock Purchase Plan $ in Millions		12 Months Ended			32 Months Ended
	May 07, 2013 period shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 shares
Stock-based compensation
Purchase price of shares expressed as percentage of fair market value of common stock	85.00%
Number of non-concurrent offering periods | period	2
Number of shares reserved (in shares)	2,500,000
Stock-based compensation expense | $		$ 0.0	$ 0.0	$ 0.0
Shares sold pursuant to the ESPP (in shares)					526,307