Employee Benefit Plans - Employee Stock Ownership Plan - Additional Information (Detail) - USD ($) $ in Millions		12 Months Ended
	Apr. 30, 2007	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
ESOP loan	$ 216.8	$ 171.8
ESOP, shares to be purchased (in shares)	10,453,575
Loan repayments expected annual through 2036		18.8
Cash dividends paid on unallocated ESOP shares		$ 4.4	$ 4.6	$ 4.8
Minimum age requirement to participate in ESOP		18 years
Minimum work experience within 12 months of hire needed to participate in ESOP		1000 hours
ESOP common stock allocated (in shares)		4,529,883
Unallocated common stock of Employee Stock Ownership Plan (in shares)		5,923,692	6,300,000
Fair value of deferred ESOP shares		$ 100.1
ESOP compensation expense		$ 5.7	$ 6.2	$ 6.4