Income taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components Of Income Tax Expense Benefit [Line Items]
Income tax (expense) benefit	$ 11,797	$ (60)	$ 11,797
Effective income tax rate benefit		0.00%	19.50%	0.00%
Approximately valuation allowance increased		$ 75,500
Earlier Tax Year [Member]
Components Of Income Tax Expense Benefit [Line Items]
Federal, state and foreign income tax returns		Dec. 31, 2012
Latest Tax Year [Member]
Components Of Income Tax Expense Benefit [Line Items]
Federal, state and foreign income tax returns		Dec. 31, 2015
Research Tax Credit Carryforward [Member]
Components Of Income Tax Expense Benefit [Line Items]
Limitations on use of net operating losses and tax credit carryforwards, percentage		50.00%
Limitations on use of net operating losses and tax credit carryforwards, period		3 years
Significant accrued interest or penalties related to uncertain tax positions		$ 0	$ 0	$ 0
Interest or penalties Expense related to uncertain tax positions		0	0	0
U.S. [Member]
Components Of Income Tax Expense Benefit [Line Items]
Operating loss carryforwards		$ 347,500	$ 130,000	$ 30,300
Operating loss carryforwards expiration year		2035	2035	2035
Credit carryforward expiration year		2035	2035	2035
U.S. [Member] | Excess Equity Based Compensation Tax Deductions
Components Of Income Tax Expense Benefit [Line Items]
Operating loss carryforwards		$ 185,800
U.S. [Member] | Research Tax Credit Carryforward [Member]
Components Of Income Tax Expense Benefit [Line Items]
Tax credit carryforward amount		44,900	$ 22,000	$ 2,700
State and Local Jurisdiction [Member]
Components Of Income Tax Expense Benefit [Line Items]
Operating loss carryforwards		$ 335,000	$ 115,500	$ 13,300
Operating loss carryforwards expiration year		2035	2035	2035
Credit carryforward expiration year		2030	2030	2030
State and Local Jurisdiction [Member] | Excess Equity Based Compensation Tax Deductions
Components Of Income Tax Expense Benefit [Line Items]
Operating loss carryforwards		$ 185,800
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward [Member]
Components Of Income Tax Expense Benefit [Line Items]
Tax credit carryforward amount		3,800	$ 2,000	$ 1,400
Foreign Tax Authority [member]
Components Of Income Tax Expense Benefit [Line Items]
Operating loss carryforwards		$ 600	2,700	$ 2,000
Excluding the impact of tax adjustments
Components Of Income Tax Expense Benefit [Line Items]
Income tax (expense) benefit			$ 0
Effective income tax rate benefit			0.00%