Debt - January 2017 Exchangeable Senior Notes - Additional Information (Detail) - Convertible Debt			6 Months Ended
	Jan. 20, 2017 USD ($) d $ / shares	Jan. 19, 2017 $ / shares	Jun. 30, 2017 USD ($) shares	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Debt Disclosure [Line Items]
Convertible senior notes, stated interest rate			3.50%
Convertible notes, interest expense				$ 6,900,000
Accrued interest on convertible note			$ 0		$ 200,000
Non Cash
Debt Disclosure [Line Items]
Convertible notes, interest expense				$ 4,000,000
2017 Notes
Debt Disclosure [Line Items]
Convertible senior notes, principal amount	$ 30,000,000		$ 30,000,000
Convertible senior notes, stated interest rate	3.50%
Convertible senior notes, due date	2047
Convertible senior notes, repurchase price at option of the issuer	100.00%
Net proceeds from offering	$ 28,800,000
Convertible senior notes, interest payable dates	payable semi-annually in arrears on January 15 and July 15 of each year, beginning on July 15, 2017
Convertible senior notes, payment start date	Jul. 15, 2017
Convertible senior notes, maturity date	Jan. 15, 2047
Convertible senior notes, percentage of premium initial exchange price		35.00%
Convertible senior notes, total ADS into which the debt is exchangeable | shares			7,716,048
Value of shares in excess of principal amount of Notes based on closing price			$ 1,100,000
Convertible senior notes, redemption start date	Jan. 19, 2021
Convertible senior notes redemption, end date	Jan. 15, 2047
Convertible senior notes, mandatory exchange in whole or in part if daily VWAP equals or exceeds percentage of exchange price	130.00%
Convertible senior notes, mandatory exchange in whole or in part if daily VWAP, stock trigger price | $ / shares	$ 5.05
Convertible senior notes, mandatory exchange in whole or in part if daily VWAP equals or exceeds percentage of exchange price, at least number of VWAP Trading days | d	20
Convertible senior notes, mandatory exchange in whole or in part if daily VWAP equals or exceeds percentage of exchange price, in any number of VWAP Trading days | d	30
Convertible senior notes, discount	$ 1,200,000		1,100,000
Convertible notes, carrying amount net of unamortized discount			28,900,000
Convertible notes, interest expense			500,000
Interest expense, contractual coupon interest			500,000
Accrued interest on convertible note			500,000
2017 Notes | Minimum
Debt Disclosure [Line Items]
Percentage of holders of principal amount required to issue notice on default	25.00%
2017 Notes | Maximum | Non Cash
Debt Disclosure [Line Items]
Convertible notes, interest expense			$ 100,000
2017 Notes | American Depositary Shares
Debt Disclosure [Line Items]
Convertible senior notes, exchange rate of ADS per $1,000 principal amount of notes	257.2016
Convertible senior notes, initial exchange price | $ / shares	$ 3.89	$ 2.88