Income Taxes - Reconciliation of Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	21.00%	35.00%	35.00%
U.S. taxation of foreign profits, net of foreign tax credits	0.30%	0.10%	1.10%
Research and employment tax credits	(9.60%)	(0.40%)	3.20%
State and local taxes	11.00%	0.20%	4.90%
Domestic production activities	4.90%	(0.40%)	1.80%
Foreign tax rate differences	5.80%	(1.00%)	4.30%
Statutory changes in tax rates	0.60%	0.30%	0.20%
Valuation allowance	(2.30%)	0.20%	(6.70%)
Nondeductible expenses	3.00%	0.30%	(1.10%)
Gain on reconsolidation of GST and OldCo	0.00%	(32.40%)	0.00%
Reconsolidation step-up of net assets of GST and OldCo to fair value	0.00%	9.00%	0.00%
GILTI	11.60%	0.00%	0.00%
Other Tax Act items	5.40%	(5.30%)	0.00%
Other items, net	(4.40%)	0.90%	(1.00%)
Effective income tax rate	47.30%	6.50%	41.70%