Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Contribution expense under employee stock ownership plan	$ 2.8	$ 1.5
Employer Matching Contribution Tranche One [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution plan, employer matching contribution percentage			75.00%
Defined contribution plans employee contribution percentage of eligible compensation matched by employer			4.00%
Employer Matching Contribution Tranche Two [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution plan, employer matching contribution percentage			50.00%
Defined contribution plans employee contribution percentage of eligible compensation matched by employer			4.00%