- Reconciliation of Federal Statutory Income Tax Rate to Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal statutory rate	35.00%	35.00%	35.00%
State income taxes, net of federal benefit	1.40%	1.40%	1.50%
Domestic manufacturing deduction	(0.50%)	(2.10%)	(0.80%)
Research and development tax credit	(5.60%)	(4.30%)	(3.10%)
Stock based compensation	(4.40%)	0.00%	0.00%
Valuation allowance for foreign subsidiaries net operating losses	1.20%	0.00%	0.20%
Tax rate changes	17.40%	0.00%	0.00%
Non-deductible expenses	2.00%	2.40%	0.40%
Other permanent differences	(0.60%)	(0.40%)	0.40%
Effective income tax rate for continuing operations	45.90%	32.00%	33.60%