Debt - January 2012, May 2014, and November 2015 Exchangeable Senior Notes - Additional Information (Detail)	1 Months Ended						3 Months Ended	12 Months Ended
	Jan. 31, 2017 USD ($)	Sep. 30, 2016 USD ($) shares	Aug. 31, 2016 USD ($) shares	Nov. 30, 2015 USD ($)	May 31, 2014 USD ($)	Jan. 31, 2012 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Debt Disclosure [Line Items]
Proceeds from issuance of convertible debt, net of transaction costs										$ 27,514,000
Convertible senior notes, principal amount									$ 128,115,000
Convertible senior notes, repayment								$ 15,107,000		16,145,000
Convertible senior notes, carrying value, exchanged									127,300,000
Carrying amount of debt conversion option									127,436,000
Transaction costs									680,000
Decrease to additional paid-in capital for repurchase of conversion option in convertible notes										(1,300,000)
Gain (loss) on change in fair value of derivative liabilities									8,170,000	(1,106,000)
Interest expense, non-cash								2,332,000	7,783,000	8,258,000
Interest								$ 17,241,000	$ 17,083,000	$ 12,559,000
Common Shares
Debt Disclosure [Line Items]
Convertible senior notes, total ADS into which the debt is exchangeable | shares									60,311,188	6,283,333
Carrying amount of debt conversion option									$ 40,062,000
Convertible Debt
Debt Disclosure [Line Items]
Convertible senior notes, stated interest rate								3.50%
Convertible senior notes, principal amount									150,000,000
Convertible notes, interest expense									9,900,000
Accrued interest on convertible note								$ 0	200,000
Interest								300,000	5,400,000
Convertible Debt | Non Cash
Debt Disclosure [Line Items]
Interest expense, non-cash									5,700,000
Convertible Debt | Cash
Debt Disclosure [Line Items]
Interest expense, contractual coupon interest								100,000	4,200,000
Convertible Debt | Common Shares
Debt Disclosure [Line Items]
Carrying amount of debt conversion option									$ 40,100,000
Convertible Debt | American Depositary Shares
Debt Disclosure [Line Items]
Convertible senior notes, total ADS into which the debt is exchangeable | shares									60,311,188
Transaction costs									$ 700,000
Convertible Debt | 2012 Notes
Debt Disclosure [Line Items]
Convertible senior notes, principal amount	$ 15,100,000			$ 15,100,000	$ 31,300,000	$ 150,000,000		0	15,100,000
Convertible senior notes, stated interest rate	3.50%					3.50%
Convertible senior notes, due date	2032					2032
Proceeds from issuance of convertible debt, net of transaction costs						$ 144,300,000
Convertible senior notes, principal amount purchase	$ 15,000,000			16,200,000			$ 15,000,000
Convertible senior notes, repurchase price at option of the issuer	100.00%					100.00%
Convertible senior notes, aggregate principal amount redeemed							$ 100,000	100,000
Convertible senior notes, outstanding amount								$ 0
Carrying amount of debt conversion option						$ 23,800,000
Decrease to additional paid-in capital for repurchase of conversion option in convertible notes					10,100,000
Note, estimated remaining life						24 months		24 months
Convertible senior notes, discount									0
Convertible Debt | 2012 Notes | Other Debt Obligations
Debt Disclosure [Line Items]
Convertible senior notes, fair value						$ 126,200,000
Convertible Debt | 2014 Notes
Debt Disclosure [Line Items]
Convertible senior notes, principal amount			$ 118,700,000		$ 118,700,000			$ 0	0
Convertible senior notes, stated interest rate					3.50%
Convertible senior notes, due date					2032
Convertible senior notes, principal amount		$ 118,700,000			$ 118,700,000
Convertible senior notes, repurchase price at option of the issuer					100.00%
Convertible senior notes, fair value					$ 90,800,000
Decrease to additional paid-in capital for repurchase of conversion option in convertible notes				1,300,000
Convertible senior notes, discount					27,900,000
Offering costs					2,500,000
Derivative liability at fair value					$ 3,500,000
Gain (loss) on change in fair value of derivative liabilities									2,100,000
Convertible Debt | 2014 Notes | American Depositary Shares
Debt Disclosure [Line Items]
Convertible senior notes, total ADS into which the debt is exchangeable | shares		47,739,925
Convertible Debt | 2014 Notes | Final As-Adjusted | American Depositary Shares
Debt Disclosure [Line Items]
Convertible senior notes, exchange rate of ADS per $1,000 principal amount of notes			402.0746
Convertible senior notes, total ADS into which the debt is exchangeable | shares			47,739,925
Convertible Debt | 2015 Notes
Debt Disclosure [Line Items]
Convertible senior notes, principal amount			$ 31,300,000	$ 31,300,000				0	0
Convertible senior notes, stated interest rate				3.50%
Convertible senior notes, due date				2032
Proceeds from issuance of convertible debt, net of transaction costs				$ 27,500,000
Convertible senior notes, principal amount		$ 31,300,000
Convertible senior notes, repayment				$ 15,900,000
Equity component of convertible notes issuance cost									87,400,000
Debt instrument increase accrued interest									800,000
Convertible senior notes, repurchase price at option of the issuer				100.00%
Convertible senior notes, fair value				$ 27,500,000
Carrying amount of debt conversion option								$ 11,500,000	11,500,000
Convertible senior notes, discount				3,800,000
Offering costs				100,000
Derivative liability at fair value				$ 500,000
Gain (loss) on change in fair value of derivative liabilities									$ 600,000
Convertible Debt | 2015 Notes | American Depositary Shares
Debt Disclosure [Line Items]
Convertible senior notes, total ADS into which the debt is exchangeable | shares		12,571,263
Convertible Debt | 2015 Notes | Final As-Adjusted | American Depositary Shares
Debt Disclosure [Line Items]
Convertible senior notes, exchange rate of ADS per $1,000 principal amount of notes			402.0746
Convertible senior notes, total ADS into which the debt is exchangeable | shares			12,571,263