XML 128 R67.htm IDEA: XBRL DOCUMENT v3.6.0.2
Income taxes - Reconciliation of Income Tax (Benefit) Provision Computed at the Statutory Federal Income Tax Rate to Effective Income Tax Rate (Benefit) Provision as Reflected in the Financial Statements (Detail)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Tax Disclosure [Abstract]      
Federal income tax expense at statutory rate 34.00% 34.00% 34.00%
State income tax, net of federal benefit 3.30% 4.20% 4.00%
Permanent differences (5.30%) (6.40%) (3.20%)
Research and development credit 15.00% 14.60% 25.70%
Foreign differential (7.00%) (1.00%) 0.00%
Other 0.00% (0.50%) 0.00%
Change in valuation allowance (39.90%) (44.90%) (41.00%)
Effective income tax rate benefit 0.10% 0.00% 19.50%