Debt Convertible Senior Notes Textual -Additional Information (Detail) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2014 USD ($) $ / shares	Sep. 30, 2015 USD ($) d	Dec. 31, 2014 USD ($) $ / shares	Dec. 08, 2014 USD ($)
Convertible Debt [Member] | Senior 3 Point 25 Percent Convertible Notes Due 2020 [Member]
Debt Instrument [Line Items]
Convertible Senior Notes, face amount	$ 172,500		$ 172,500
Senior Credit Facility, applicable margin		3.25%
Debt issuance cost	5,100
Deferred financing costs	$ 4,200		$ 4,200
Remaining amortization period of discount on the liability component		5 years 4 months	6 years
Adjustments to additional paid in capital		$ 900
Convertible Senior Notes, conversion ratio		31.1891
Convertible Senior Notes, conversion price | $ / shares	$ 32.06		$ 32.06
Convertible Senior Notes, threshold trading days | d		20
Convertible Senior Notes, threshold consecutive trading days		30 days
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
Amortization of debt discount (premium)		4,000
Interest expense, Convertible Senior Notes, excluding amortization		$ 4,200
Debt Conversion, Converted Instrument, Rate		100.00%
Debt Instrument, Interest Rate, Effective Percentage		6.90%
Convertible Senior Notes, fair value disclosures	$ 141,900		$ 141,900
Carrying value of equity component, net of issuance costs	29,758	$ 29,758	29,758	$ 30,700
Other Current Assets [Member]
Debt Instrument [Line Items]
Deferred financing costs	300	300	300
Other Current Assets [Member] | Senior 3 Point 25 Percent Convertible Notes Due 2020 [Member]
Debt Instrument [Line Items]
Deferred financing costs	600		600
Other Current Assets [Member] | Convertible Debt [Member] | Senior 3 Point 25 Percent Convertible Notes Due 2020 [Member]
Debt Instrument [Line Items]
Deferred financing costs	4,139	3,661	4,139
Other non-current assets [Member]
Debt Instrument [Line Items]
Deferred financing costs	500	$ 300	500
Other non-current assets [Member] | Senior 3 Point 25 Percent Convertible Notes Due 2020 [Member]
Debt Instrument [Line Items]
Deferred financing costs	$ 3,500		$ 3,500