Debt Obligations - Additional Information (Details) - 1.75% Convertible Senior Notes Due 2022	1 Months Ended	3 Months Ended
	Nov. 30, 2017 USD ($) d $ / shares shares	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Line Of Credit Facility [Line Items]
Debt instrument aggregate principal amount	$ 200,000,000
Debt instrument maturity year	2022
Debt instrument fixed interest rate per annum	1.75%
Debt instrument, frequency of payment		Payable semi-annually in arrears on June 1 and December 1 of each year, commencing on June 1, 2018.
Net proceeds from the debt offering, after deducting transaction costs	$ 193,800,000
Convertible notes, shares issued | shares	57.6037
Convertible notes, principal amount	$ 1,000
Convertible notes, initial conversion price | $ / shares	$ 17.36
Convertible notes, type of equity security issued		Common stock
Convertible notes, conversion description		Holders of the notes may convert their notes at their option at any time prior to the close of business on the business day immediately preceding September 1, 2022, only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on March 31, 2018 (and only during such calendar quarter), if the last reported sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (2) during the five-business day period after any five consecutive trading day period (the “measurement period”) in which the trading price per $1,000 principal amount of notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate for the notes on each such trading day; (3) if the Company calls any or all of the notes for redemption, at any time prior to the close of business on the scheduled trading day immediately preceding the redemption date; or (4) upon the occurrence of specified corporate events. On or after September 1, 2022, holders may convert all or any portion of their notes at any time prior to the close of business on the scheduled trading day immediately preceding the maturity date regardless of the foregoing conditions. Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election. The Company intends to settle the principal amount of the notes with cash.
Convertible notes, percentage of conversion price	130.00%
Convertible notes, redemption description		The Company may not redeem the notes prior to December 5, 2020. It may redeem for cash all or any portion of the notes, at its option, on or after December 5, 2020 if the last reported sale price of its common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period (including the last trading day of such period) ending not more than three trading days preceding the date on which it provides notice of redemption at a redemption price equal to 100% of the principal amount of the notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date.
Convertible notes, redemption percentage	100.00%
Convertible notes, sinking fund	$ 0
Percentage of repurchase price is equal to principal amount of convertible notes	100.00%
Carrying amount of the liability component	$ 149,300,000
Carrying amount of the equity component	$ 50,700,000
Convertible notes, effective interest rate	5.80%
Debt issuance costs	$ 6,200,000
Amortization of interest expense	4,600,000	$ 229,000
Adjustments to additional paid in capital, equity component of debt issuance costs	$ 1,600,000	1,600,000	$ 1,600,000
Additional Paid-In Capital
Line Of Credit Facility [Line Items]
Carrying amount of the equity component		$ 49,100,000	$ 49,100,000
90% Applicable Conversion Price
Line Of Credit Facility [Line Items]
Convertible notes, consecutive trading days | d	5
Minimum | 130% Applicable Conversion Price
Line Of Credit Facility [Line Items]
Convertible notes, consecutive trading days | d	20
Maximum
Line Of Credit Facility [Line Items]
Convertible notes, percentage of last reported sale price of common stock	98.00%
Maximum | 130% Applicable Conversion Price
Line Of Credit Facility [Line Items]
Convertible notes, consecutive trading days | d	30