Senior Secured Notes - Additional Information (Detail) - USD ($)		12 Months Ended
	Oct. 05, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Cash paid for interest		$ 20,589,000	$ 20,225,000	$ 17,445,000
Loss on extinguishment of debt		0	14,079,000	0
Write-off of unamortized issuance costs		$ 0	1,579,000	$ 0
Percentage of repurchase of notes on principal amount of notes		101.00%
Percentage of repurchase of notes on principal amount of notes upon sale of assets		100.00%
Senior secured notes, principal amount		$ 250,000,000
7.75% Senior Secured Notes Due October 2020 [Member]
Line of Credit Facility [Line Items]
Senior secured notes, interest rate		7.75%
Senior Notes [Member] | 7.75% Senior Secured Notes Due October 2020 [Member]
Line of Credit Facility [Line Items]
Senior secured notes, issued	$ 250,000,000
Senior secured notes, interest rate	7.75%	7.75%
Senior secured notes, maturity date		Oct. 05, 2020
Frequency of payment		Quarterly
Issuance costs	$ 8,900,000
Debt discount on transaction and facility fees	8,700,000
Unamortized debt discount and issuance costs		$ 6,500,000
Debt instrument term		5 years
Senior secured notes, cash received	$ 100,300,000
Minimum cash and investments in marketable securities to be maintained		$ 60,000,000
Senior Notes [Member] | 7.75% Senior Secured Notes Due October 2020 [Member] | Level 3 [Member]
Line of Credit Facility [Line Items]
Senior secured notes, principal amount		$ 250,000,000
Senior Notes [Member] | 12% Senior Secured Notes Due July 2017 [Member]
Line of Credit Facility [Line Items]
Senior secured notes, interest rate	12.00%
Senior secured notes, maturity date	Jul. 15, 2017
Repayment of senior secured notes	$ 125,000,000
Accrued interest paid on 12% notes at redemption	3,300,000
Redemption premium	12,500,000		11,300,000
Cash paid for interest	$ 1,200,000		1,200,000
Loss on extinguishment of debt			14,100,000
Write-off of unamortized issuance costs			$ 1,600,000