Convertible Senior Notes - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 30, 2014	Jul. 31, 2013	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	May 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long term debt, face amount			$ 212,305		$ 212,305					$ 215,000
Other long term assets			2,423		2,423					3,125	[1]
Convertible senior notes, net			207,933		207,933					209,166	[1]
Amortization of debt issuance costs recognized as interest expense			400	$ 400	1,500	$ 1,200
4.25% Convertible Senior Notes (due 2018)
Debt Instrument [Line Items]
Long term debt, face amount		$ 100,000	$ 99,305		$ 99,305					$ 100,000
Debt instrument, interest rate		4.25%	4.25%		4.25%					4.25%
Debt instrument, maturity date		Aug. 01, 2018
Frequency of interest payment					Semi-annually
Conversion rate in share per $1000 principal amount of notes		114.3674
Debt instrument, conversion rate		$ 8.74
Debt instrument repurchase amount							$ 700	$ 700
Convertible senior notes, net			$ 97,844		$ 97,844					$ 97,819
Convertible senior note payable, fair value			111,800		111,800					102,000
4.875% Convertible Senior Notes (due 2020)
Debt Instrument [Line Items]
Long term debt, face amount	$ 115,000		$ 113,000		$ 113,000					$ 115,000
Debt instrument, interest rate	4.875%		4.875%		4.875%					4.875%
Debt instrument, maturity date	Jun. 01, 2020
Frequency of interest payment					Semi-annually
Conversion rate in share per $1000 principal amount of notes	103.7613
Debt instrument, conversion rate	$ 9.64
Debt instrument repurchase amount									$ 2,000
Convertible senior notes, net			$ 110,089		$ 110,089					$ 111,347
Convertible senior note payable, fair value			$ 120,000		$ 120,000					112,300
ASU 2015-03 | Restatement Adjustment
Debt Instrument [Line Items]
Other long term assets										(5,800)
Convertible senior notes, net										$ 5,800

[1] Derived from audited financial statements