Convertible Senior Notes - Convertible Notes and Options (Details) $ / shares in Units, shares in Millions		1 Months Ended	2 Months Ended	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares	May 31, 2018 USD ($) day $ / shares shares	Jun. 30, 2018 USD ($)	Dec. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Proceeds from issuance of convertible senior notes, net of issuance costs				$ 0	$ 138,854,000	$ 0
Net carrying amount	$ 117,178,000			117,178,000	110,540,000
Total interest expense				8,789,000	5,241,000	0
Capped Calls, initial strike price (in dollars per share) | $ / shares		$ 32.25
Capped Calls, initial cap price (in dollars per share) | $ / shares		$ 38.94
Capped Calls, number of shares covered | shares		4.5
Payments To Purchase Capped Calls		$ 8,900,000		0	8,907,000	$ 0
Convertible Debt | Convertible Senior Notes at 1.50%
Debt Instrument [Line Items]
Aggregate principal amount	143,750,000	$ 143,750,000		143,750,000	143,750,000
Stated interest rate		1.50%
Proceeds from issuance of convertible senior notes, net of issuance costs		$ 138,900,000
Unamortized debt discount	(23,880,000)			(23,880,000)	(29,846,000)
Unamortized issuance costs	(2,692,000)			(2,692,000)	(3,364,000)
Net carrying amount	117,178,000			117,178,000	110,540,000
Convertible Debt | Convertible Senior Notes At 1.50%, Option Portion
Debt Instrument [Line Items]
Aggregate principal amount		$ 18,750,000
Stated interest rate		1.50%
Convertible debt, conversion price (in dollars per share) | $ / shares		$ 32.25
Denominator in calculation of trading price		$ 1,000
Conditional cash repurchase, percent of principal		100.00%
Carrying amount of the equity component	33,350,000	$ 33,400,000		33,350,000	33,350,000
Debt discount effective interest rate			7.60%
Amortization of debt issuance costs			$ 4,900,000	673,000	395,000
Amortization of debt issuance costs, liability component			3,800,000
Amortization of debt issuance costs, equity component			$ 1,100,000
Issuance costs	(1,136,000)			(1,136,000)	(1,136,000)
Net carrying amount	32,214,000			32,214,000	32,214,000
Estimated fair value of the Notes	142,400,000			142,400,000
Denominator in closing price calculation	$ 100			$ 100
If-converted value, share price (in dollars per share) | $ / shares	$ 20.76			$ 20.76
If-converted value of the Notes	$ 92,500,000
Contractual interest expense				$ 2,150,000	1,342,000
Amortization of debt discount				5,966,000	3,504,000
Total interest expense				$ 8,789,000	$ 5,241,000
Convertible Debt | Convertible Senior Notes At 1.50%, Option Portion | Maximum
Debt Instrument [Line Items]
Convertible debt, threshold trading days | day		20
Convertible debt, threshold consecutive trading days | day		30
Percent of conversion price triggering conversion feature		130.00%
Convertible Debt | Convertible Senior Notes At 1.50%, Option Portion | Minimum
Debt Instrument [Line Items]
Convertible debt, threshold trading days | day		5
Convertible debt, threshold consecutive trading days | day		10
Percent of conversion price triggering conversion feature		98.00%