Performance-Based Common Stock Warrants - Narrative (Details)		9 Months Ended
	Mar. 09, 2016 USD ($) vesting_period $ / shares shares	Sep. 30, 2019 USD ($) shares
Class of Warrant or Right [Line Items]
Unrecognized estimated fair value of unvested warrants | $		$ 6,400,000
Common Stock Purchase Warrants
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 vesting periods	2 years	2 years
Vesting period one	2 years
Vested warrants outstanding (in shares) | shares		175,000
Unearned underlying shares (in shares) | shares		475,000
Number of warrants vested (in shares) | shares		0
Common Stock Purchase Warrants | Supply Threshold
Class of Warrant or Right [Line Items]
Aggregate level of purchases, $260 million threshold | $	$ 260,000,000
Aggregate level of purchases, $340 million threshold | $	$ 340,000,000
Supply threshold amount | $		$ 680,000,000