Credit Facility and Convertible Debentures - Convertible Senior Debentures Narrative (Detail) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Nov. 30, 2012
Debt Instrument [Line Items]
Repurchase of convertible senior debentures				$ 677,000
Convertible senior debentures - current	$ 42,320,000	$ 42,320,000		42,320,000		$ 0
Convertible Debt [Member]
Debt Instrument [Line Items]
Aggregate face value of convertible senior debentures	43,600,000	43,600,000		43,600,000			$ 55,000,000.0
Interest rate on debentures							5.25%
Repurchased face amount	11,400,000	11,400,000		11,400,000
Repayments of long-term debt	11,800,000
Loss on extinguishment of debt	0
Gross carrying amount of equity component	5,800,000	5,800,000		5,800,000
Principal amount outstanding	43,600,000	43,600,000		43,600,000
Unamortized discount	1,000,000	1,000,000		1,000,000
Deferred finance costs, noncurrent, net	300,000	300,000		300,000
Convertible senior debentures - current	$ 42,300,000	42,300,000		42,300,000
Amortization of debt discount (premium)		$ 400,000	$ 300,000	$ 900,000	$ 600,000
Debt instrument, interest rate, effective percentage	8.70%	8.70%		8.70%
Fair value of debentures outstanding	$ 45,100,000	$ 45,100,000		$ 45,100,000
Additional Paid-in Capital
Debt Instrument [Line Items]
Repurchase of convertible senior debentures				$ 677,000