Income Taxes - Additional Information (Detail) - USD ($)		12 Months Ended
	Jan. 01, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 01, 2019
Income Tax Examination [Line Items]
Deferred income tax (benefit) expense		$ 0
Postretirement benefit obligations		1,600,000	$ 1,200,000
Derivatives		5,009,000	182,000
Unrealized losses on investments in debt and equity		19,000,000.0	8,700,000
Deferred tax asset		49,212,000	18,244,000
Unrecognized tax benefits		0
Excess income tax benefits from stock compensation		100,000	2,000,000.0	$ 3,500,000
Income tax credit and deferred tax asset	$ 8,500,000
Tax expense (benefit) from CARES Act		1,700,000
Amortization of low-income housing credit investments reflected as income tax expense		3,300,000	3,000,000.0	$ 1,900,000
Affordable housing tax benefits		900,000
Carrying value of investment in affordable housing credits		26,600,000	$ 25,800,000
Federal
Income Tax Examination [Line Items]
Net operating loss carryforwards		600,000
Federal net operating loss		100,000
General Business Tax Credit Carryforward
Income Tax Examination [Line Items]
Tax credit		2,900,000
Beneficial
Income Tax Examination [Line Items]
Deferred tax asset					$ 18,900,000
Unrecognized tax benefits		$ 1,700,000