Borrowings - Convertible Notes - Additional Information (Detail)							1 Months Ended	2 Months Ended	3 Months Ended	12 Months Ended
	Sep. 05, 2017 shares	Aug. 11, 2017 shares	May 26, 2017	Apr. 18, 2016 shares	Apr. 13, 2016 USD ($) shares	Jul. 31, 2013 USD ($) $ / shares	Jul. 31, 2013 USD ($) $ / shares	Nov. 30, 2017 USD ($) $ / shares	Jun. 30, 2016 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Principal amount of convertible notes due 2020 converted into shares of common stock											$ 64,209,000
Common stock, shares issued | shares	13,280,000	132,800,000								13,343,000	13,020,000
Loss on extinguishment of debt										$ 5,202,000	$ 14,566,000
Debt maturity date										Jul. 15, 2020
Reverse stock split description		Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock								Reverse Split, every ten shares of common stock issued and outstanding was converted into one share of common stock
Reverse stock split, conversion ratio		0.1
Interest expense										$ 34,650,000	22,449,000	$ 18,769,000
Convertible Notes [Member]
Debt Instrument [Line Items]
Aggregate principal amount						$ 125,000,000	$ 125,000,000
Net proceeds from the debt issuance							$ 120,600,000
Interest rate (as a percent)						4.50%	4.50%
Embedded conversion option						$ 53,800,000	$ 53,800,000
Underwriting discounts and commissions and offering expenses						4,400,000
Principal amount of convertible notes due 2020 converted into shares of common stock					$ 64,200,000
Conversion ratio, principal amount					$ 1,000	$ 1,000	$ 1,000
Conversion rate of common stock shares per $1,000 principal amount	23.5210		235.2112	14		160
Common stock, shares issued | shares				873,215	363,551				1,236,766
Value of additional shares issued for conversion					$ 27,700,000
Trading period					10 days
Increase to additional paid in capital pursuant to conversion									$ 101,000,000
Loss on extinguishment of debt									14,600,000	300,000
Reduction in additional paid-in capital attributable to embedded conversion option									39,800,000	$ 4,200,000
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be convertible						30 days
Convertibility of debt, closing price of stock test, percentage of stock price to conversion price for the notes that must be exceeded						130.00%
Number of consecutive business days immediately after any five consecutive trading day period during the note measurement period						5 days
Number of consecutive trading days before five consecutive business days during the note measurement period						5 days
Initial conversion price of shares (in dollars per share) | $ / shares						$ 6.25	$ 6.25
Reverse stock split description										one-for-ten reverse stock split
Reverse stock split, conversion ratio	0.1
Minimum percentage of aggregate principal amount held by bondholders to declare notes due and payable						25.00%
Percentage of principal amount due and payable upon event of default						100.00%
Interest expense										$ 9,200,000	$ 22,700,000	$ 13,700,000
Debt instrument, transaction costs								$ 3,800,000		3,500,000
Repayment of debt								59,100,000
Accrued and unpaid interest								700,000
Purchase of convertible notes								$ 60,800,000
Offering amount of per unit debt instrument issued at discount | $ / shares								900
Principal amount of per unit debt instrument issued at discount | $ / shares								1,000
Convertible Notes [Member] | Conversion Terms, Fundamental Changes [Member]
Debt Instrument [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest						100.00%
Convertible Notes [Member] | Conversion Terms, Event of Default [Member]
Debt Instrument [Line Items]
Percentage of principal amount due and payable upon event of default arising out of certain bankruptcy events						100.00%
Convertible Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be convertible						20 days
Convertible Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Convertibility of debt, trading price of debt test, percentage of closing price of stock used in calculation						98.00%
Convertible Notes [Member] | Transaction Costs Incurred With Third Parties [Member]
Debt Instrument [Line Items]
Reduction in additional paid-in capital									200,000	300,000
Convertible Notes [Member] | Interest Expense [Member]
Debt Instrument [Line Items]
Loss on extinguishment of debt										300,000
Convertible Notes [Member] | Interest Expense [Member] | Transaction Costs Incurred With Third Parties [Member]
Debt Instrument [Line Items]
Transaction costs related to conversion of convertible notes due 2020 incurred and paid									$ 200,000	$ 3,500,000