Reconciliation of Effective Income Tax Rate from Statutory Federal Income Tax Rate (Detail)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Effective Income Tax Rate [Line Items]
Statutory federal income tax rate		35.00%	35.00%	35.00%
Valuation allowance		1.20%	0.30%	0.70%
Transaction costs			1.10%
State income taxes, net of federal benefit and tax credits		(4.50%)	3.70%	4.60%
Permanent differences		2.70%	2.20%	1.10%
Domestic production activities			(3.20%)	(3.10%)
Federal research and experimentation credits		(9.10%)	(2.30%)	(1.20%)
Tax effects of foreign activities		(1.10%)	5.20%	2.00%
Tax-exempt income		(0.30%)	(0.30%)	(0.10%)
Provision to return adjustments		(5.20%)	0.30%	0.30%
Non-deductible compensation		5.00%	6.20%	3.30%
Provision for uncertain tax positions		0.70%	(2.30%)	(2.60%)
Excess tax benefits related to share-based compensation		(66.00%)	(20.10%)
Net deferred tax assets re-measurement	[1]	51.80%
Other		1.00%	(2.50%)
Effective income tax rate		11.20%	23.30%	40.00%

[1] Due to the impact of the Tax Reform Act.