Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended			65 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2018
Income Tax Contingency [Line Items]
Foreign tax rate and other foreign related tax items	$ (13,539)	$ (20,415)	$ (25,976)
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 46,200	$ 22,100
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	25.00%	35.00%
Stock Repurchased During Period, Value	$ 136,100	$ 99,100	197,500	$ 942,700
Document Period End Date	Sep. 30, 2018
Income tax expense (benefit)	$ 56,807	(31,981)	(14,197)
Undistributed earnings of foreign subsidiaries	310,500			310,500
Deferred tax assets valuation allowance	183,295	229,449		183,295
Unrecognized tax benefits potential to favorably impact effective tax rate	$ 30,400			30,400
Significant change in unrecognized tax benefits is not expected, period	12 months
Unrecognized tax benefits, interest and penalties accrued	$ 10,800	9,900		10,800
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	1,400	2,100	$ 2,200
Investment Tax Credit Carryforward [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards	14,700	14,800		14,700
United States
Income Tax Contingency [Line Items]
Deferred tax assets valuation allowance	142,800	202,300		142,800
Net operating loss carryforwards	692,900	642,000		692,900
United States | Research and Development
Income Tax Contingency [Line Items]
Net operating loss carryforwards	30,200	43,500		30,200
State
Income Tax Contingency [Line Items]
Net operating loss carryforwards	259,100	262,700		259,100
State | Research and Development
Income Tax Contingency [Line Items]
Net operating loss carryforwards	5,300	6,200		5,300
Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Deferred tax assets valuation allowance	40,500	27,100		40,500
Net operating loss carryforwards	$ 164,900	$ 168,800		$ 164,900
Minimum
Income Tax Contingency [Line Items]
Tax Credit Carryforward, Expiration Date	Oct. 01, 2018