Debt Convertible Senior Notes Textual -Additional Information (Detail)		3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 06, 2017 USD ($) covenant	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) d $ / shares	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2017	Dec. 08, 2014 USD ($)
Debt Instrument [Line Items]
Senior Credit Facility, applicable margin		3.25%		3.25%
Repayments of convertible debt			$ 4,459,000	$ 0
Gain on extinguishment of Convertible Senior Notes			$ (421,000)	$ 0
Convertible Debt [Member] | Senior 3 Point 25 Percent Convertible Notes Due 2020 [Member]
Debt Instrument [Line Items]
Convertible Senior Notes, face amount							$ 172,500,000.0
Senior Credit Facility, applicable margin		3.25%		3.25%
Debt issuance cost							5,100,000
Deferred financing costs							$ (4,200,000)
Remaining amortization period of discount on the liability component				3 years 3 months		4 years	6 years
Adjustments to additional paid in capital				$ 900,000
Convertible Senior Notes, conversion ratio				31.1891
Convertible Senior Notes, conversion price (in usd per share) | $ / shares		$ 32.06		$ 32.06
Convertible Senior Notes, threshold trading days | d				20
Convertible Senior Notes, threshold consecutive trading days | d				30
Convertible Senior Notes, threshold percentage of stock price trigger				130.00%
Convertible Senior Notes, threshold consecutive business days				5 days
Convertible Senior Notes, threshold consecutive trading days, following consecutive business days				5 days
Convertible Senior Notes, threshold percentage of stock price trigger, following consecutive business days				98.00%
Convertible Senior Notes, observation period				25 days
Interest expense, debt				$ 8,200,000	$ 8,200,000
Amortization of debt discount (premium)				4,100,000
Interest expense				$ 4,100,000
Converted instrument, rate				100.00%
Interest rate		6.90%		6.90%
Convertible Senior Notes, fair value disclosures							$ 141,900,000
Carrying value of equity component, net of issuance costs		$ 29,211,000		$ 29,211,000		$ 29,211,000			$ 30,700,000
Repurchase of convertible debt				5,200,000
Repayments of convertible debt				4,500,000
Repayments of Debt		4,400,000
Equity component of convertible debt,				500,000
Gain on extinguishment of Convertible Senior Notes		(400,000)
Other Current Assets [Member] | Convertible Debt [Member] | Senior 3 Point 25 Percent Convertible Notes Due 2020 [Member]
Debt Instrument [Line Items]
Deferred financing costs		$ (2,258,000)		$ (2,258,000)		$ (2,753,000)
Subsequent Event [Member]
Debt Instrument [Line Items]
Initial applicable LIBOR loan rate	3.50%
Proceeds from Lines of Credit	$ 10,000,000
Secured debt	$ 245,000,000
Applicable base loan rate	1.50%							2.50%
Additional borrowing capacity	$ 50,000,000
Percentage of excess cash flow	50.00%
Consolidated senior secured leverage ratio	1.25
Percentage net cash proceeds	100.00%
Percentage of net cash proceeds of sale leaseback transaction	30.00%
Number of financial covenants | covenant	2
Consolidated leverage ratio, period one	5.00
Consolidated leverage ratio, period two	4.25
Consolidated leverage ratio, period three	3.50
Consolidated fixed charge coverage ratio	1.25