Stockholders' Equity - Equity Incentive Plans (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($) item shares	Jun. 30, 2016 shares
Equity Incentive Plans
Number of equity incentive plans | item	2
Amended and Restated Equity Incentive Plan (The 1999 Plan)
Options disclosures
Granted (in shares)	0
2015 Plan
Equity Incentive Plans
Maximum number of shares authorized to be issued (in shares)	6,150,000
Options disclosures
Granted (in shares)	1,900,000	1,600,000
Restricted stock units
Restricted stock units disclosures
Aggregate grant date fair value | $	$ 2.4