Income Taxes - Reconciliation of the Federal Statutory Tax Rate to the Total Tax Provision (Detail)			12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Federal income taxes computed at the statutory rate	21.00%	35.00%	21.00%	24.30%
State income taxes, net of federal benefit			1.60%	1.40%
Change in current tax rate				(2.90%)
Change in deferred tax rate				(2.30%)
Research & development tax refunds & credits			(1.90%)	(1.80%)
Dividend received deduction			(0.60%)	(0.90%)
Domestic production activities deduction				(1.20%)
Incentive stock options			0.20%	(1.00%)
Other, net			0.20%	0.10%
Effective income tax rate			20.50%	15.70%