- Reconciliation of Federal Statutory Income Tax Rate to Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal statutory rate	21.00%	35.00%	35.00%
State income taxes, net of federal benefit	1.90%	1.40%	1.40%
Domestic manufacturing deduction	(1.40%)	(0.50%)	(2.10%)
Research and development tax credit	(3.10%)	(5.60%)	(4.30%)
Stock based compensation	(1.40%)	(4.40%)	0.00%
Valuation allowance	0.20%	1.20%	0.00%
Tax Reform impact	0.40%	17.40%	0.00%
Non-deductible expenses	0.00%	2.00%	2.40%
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent	1.30%	(0.30%)	(1.60%)
Other permanent differences	3.00%	(0.30%)	1.20%
Effective income tax rate for continuing operations	21.90%	45.90%	32.00%