Long-term Debt (Details) - Senior Notes - Convertible Senior Notes due 2021 $ / shares in Units, shares in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($) shares $ / shares	Dec. 31, 2016 USD ($) $ / shares
Debt Instrument [Line Items]
Face amount	$ 125,000,000	$ 125,000,000
Interest rate	2.00%	2.00%
Proceeds from issuance of debt	$ 120,200,000
Debt issuance costs	$ 4,800,000	$ 4,800,000
Repurchase price due to fundamental change as percentage of principal amount	100.00%
Interest expense		200,000
Amortization of deferred financing costs (less than)		$ 100,000
Debt conversion denominator shares per principal amount	$ 1,000
Class A | Common Stock
Debt Instrument [Line Items]
Initial conversion rate	0.0416082
Conversion price (in dollars per share) | $ / shares	$ 24.03	$ 24.03
Initial conversion amount (in shares) | shares	5.2