Performance-Based Common Stock Warrants - Additional Disclosures (Details) - Common stock purchase warrant	Mar. 09, 2016 USD ($) vesting_period $ / shares shares	Sep. 30, 2017 USD ($) shares
Class of Warrant or Right [Line Items]
Number of shares called by warrants (in shares) | shares	725,000
Exercise price of warrants (in dollars per share) | $ / shares	$ 54.55
Number of vesting periods | vesting_period	3
Term of successive voting periods (in years)	2 years
Vesting period one (in years)	2 years
Total vesting period (in years)	6 years
Warrants vested (in shares) | shares		100,000
Unrecognized fair value of unvested warrants		$ 14,200,000
Supply threshold
Class of Warrant or Right [Line Items]
Supply threshold level one, amount	$ 260,000,000
Supply threshold level three, amount	340,000,000
Supply threshold, amount	$ 1,020,000,000.00