Credit Facility and Convertible Debentures - Convertible Senior Debentures Narrative (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Nov. 30, 2012
Debt Instrument [Line Items]
Repurchase of convertible senior debentures			$ 826,000
Convertible senior debentures - current	$ 40,148,000		40,148,000		$ 0
Additional Paid-in Capital
Debt Instrument [Line Items]
Repurchase of convertible senior debentures			826,000
Convertible Debt
Debt Instrument [Line Items]
Aggregate face value of convertible senior debentures	41,000,000		41,000,000			$ 55,000,000.0
Interest rate on debentures						5.25%
Repurchased face amount	14,000,000		14,000,000
Repayments of long-term debt			14,500,000
Loss on extinguishment of debt			0
Gross carrying amount of equity component	5,700,000		5,700,000
Principal amount outstanding	41,000,000		41,000,000
Deferred finance costs, noncurrent, net	900,000		900,000
Convertible senior debentures - current	40,100,000		40,100,000
Amortization of debt discount (premium)	$ 400,000	$ 400,000	$ 1,600,000	$ 1,200,000
Debt instrument, interest rate, effective percentage	8.70%		8.70%
Fair value of debentures outstanding	$ 42,200,000		$ 42,200,000