Income Taxes - Reconciliation of Federal Statutory Tax Rate to Company's Effective Tax Rate (Detail)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Federal statutory tax rate	35.00%	35.00%	35.00%
State and local income taxes, net of federal tax benefit	(2.60%)	1.50%	(3.60%)
Effect of foreign and Puerto Rico earnings and foreign tax credits	(40.80%)	(23.70%)	(24.50%)
Effect of Research Credits and Domestic Production Activities	(2.70%)	(4.40%)	(1.60%)
Effect of change in accounting for excess tax benefit relating to share-based compensation	7.90%	0.00%	0.00%
Other, net	6.30%	0.70%	0.60%
Total	(12.70%)	9.10%	5.90%