Income taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
U.S. net operating loss carryforwards	$ 106,064	$ 62,844
Foreign net operating loss carryforwards		194
Tax credit carryforwards	87,117	47,386
Capitalized research and development expenses, net	631	979
Capital lease	47,191	24,315
Deferred revenue	18,231	16,438
Capitalized license fees	11,752	5,488
Accruals and other	32,172	19,486
Total deferred tax assets	303,158	177,130
Intangible assets	(8,129)	(9,606)
Fixed assets	(48,902)	(26,681)
Less valuation allowance	$ (246,127)	$ (140,843)