Debt - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) shares $ / shares
Senior Secured Notes Due 2022 | Convertible Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount		$ 440,000,000
Interest rate		10.75%
Redemption price, percent of principal amount of notes redeemed		100.00%
Percent of notes with option to redeem		35.00%
Redemption price, percentage of principal amount		110.75%
Redemption price if required collateral coverage ratio not met, percentage of principal amount		100.00%
Minimum collateral coverage ratio		1.5
Collateral coverage ratio, amount added to cash and cash equivalents		4.75
Collateral coverage ratio, multiplier for Average Grantor EBITDA for seven most recent fiscal quarters		4
Period to redeem notes without default if required collateral coverage ratio not met		90 days
Redemption price if company experiences change of control, percent of principal amount		101.00%
5.50% convertible senior notes due 2021
Debt Instrument [Line Items]
Aggregate principal amount			$ 1,000
5.50% convertible senior notes due 2021 | Convertible Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount	$ 213,500,000	$ 213,500,000	$ 213,500,000.0
Interest rate	5.50%		5.50%
Effective interest rate			9.50%
Debt conversion rate (in shares) | shares			102.4249
Total number of convertible shares (in shares) | shares			21,867,716
Conversion price (in usd per share) | $ / shares	$ 12.75		$ 9.76
Payments for capped call transactions			$ 27,300,000
Conversion premium percentage	60.00%		22.50%
Credit Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Borrowings outstanding	$ 0
Maximum borrowing capacity	125,000,000
Accordion feature increase limit	150,000,000
Available borrowings	$ 113,100,000
Springing maturity date, period prior to maturity date of convertible debt	91 days
Springing maturity date, period prior to maturity date of secured debt	60 days
Credit Agreement | Letter of Credit
Debt Instrument [Line Items]
Letters of credit outstanding	$ 4,700,000
Maximum borrowing capacity	$ 30,000,000
Credit Agreement | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Requirement to maintain minimum fixed charge coverage ratio, availability threshold, percent of lenders' commitments under facility	10.00%
Requirement to maintain minimum fixed charge coverage ratio, availability threshold	$ 15,000,000
Amount of aggregate default under other debt that would trigger event of default	$ 50,000,000