Retirement Plans - Aggregate Amounts of Contributions to the 401(k) and ESOP Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Plan Disclosure [Line Items]
Total contributions	$ 6,675	$ 6,929	$ 6,538
401(k) contributions [Member]
Defined Contribution Plan Disclosure [Line Items]
Aggregate amounts of contributions	2,986	2,526	2,465
ESOP contributions [Member]
Defined Contribution Plan Disclosure [Line Items]
Aggregate amounts of contributions	$ 3,689	$ 4,403	$ 4,073