Equity (Details)			1 Months Ended		12 Months Ended
		Dec. 05, 2018 USD ($) shares	Jan. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2019 USD ($) class_of_stock vote $ / shares shares		Dec. 31, 2018 USD ($) $ / shares shares		Dec. 31, 2017 USD ($) shares	May 05, 2019 USD ($)	Feb. 20, 2018 USD ($)
Class of Stock [Line Items]
Number of classes of stock | class_of_stock					1
Common stock, par value (in dollars per share) | $ / shares				$ 0.001	$ 0.001		$ 0.001
Common stock authorized (shares) | shares					250,000,000.0
Number of votes entitled to for each common share | vote					1
Preferred stock authorized (shares) | shares					5,000,000.0
Preferred stock issued (shares) | shares					0
Preferred stock outstanding (shares) | shares					0
Accretion of unamortized discount and beneficial conversion feature							$ 17,567,000	[1]	$ 3,532,000
Net increase in dividend equivalents on Series A convertible preferred shares					$ 0	[2]	$ 11,429,000		3,532,000
Shares repurchased (shares) | shares							100,000
Cash payment to repurchase Series A Preferred shares					0		$ 183,724,000		0
Excess over carrying value	[2]				0		$ 108,224,000		$ 12,000,000
Preferred shares converted into common stock (shares) | shares		100,000					100,000
Inducements paid		$ 12,000,000.0	$ 3,000,000.0	$ 15,000,000.0	$ 3,000,000.0		$ 12,000,000.0
Other costs							$ 500,000
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock authorized (shares) | shares					1,000,000.0
Preferred stock, par value (in dollars per share) | $ / shares					$ 0.001
Preferred stock issued (shares) | shares					0
Preferred stock outstanding (shares) | shares					0
Accretion of unamortized discount and beneficial conversion feature		14,700,000
Settlement of beneficial conversion feature		6,100,000
Net increase in dividend equivalents on Series A convertible preferred shares		$ 8,600,000
Shares repurchased (shares) | shares		100,000
Carrying value of preferred stock		$ 100,000,000.0
Cash payment to repurchase Series A Preferred shares		183,700,000
Excess over carrying value		$ 83,700,000
Common Stock
Class of Stock [Line Items]
Common stock authorized for repurchase											$ 500,000,000.0
Increase in amounts authorized for repurchase										$ 500,000,000.0
Stock repurchased during period (shares) | shares					6,100,000		3,600,000		5,700,000
Stock repurchased during period					$ 147,200,000		$ 63,100,000		$ 50,000,000.0
Remaining authorization to repurchase					$ 508,600,000
Common Stock
Class of Stock [Line Items]
Number of shares issued upon conversion (shares) | shares		6,896,548					6,897,000	[3]

[1] Represents total accretion of $17.6 million, net of $6.1 million acquired value of beneficial conversion feature attributable to repurchased Series A Convertible Preferred Stock.

[2] On December 5, 2018, all issued and outstanding shares of Series A Convertible Preferred Stock were repurchased in exchange for cash or converted to common stock. As a result, amounts reported for the year ended December 31, 2018, include amounts resulting from the repurchase and conversion, in addition to dividends, payments to induce conversion, and accretion of dividend equivalents prior to December 5, 2018.

[3] Represents the issuance of common stock upon conversion of 100,000 shares of Series A Convertible Preferred Stock.