Income Taxes - Summary of Reconciliation of Statutory Federal Tax and Effective Income Tax Rates (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Income Taxes Summary Of Reconciliation Of Statutory Federal Tax And Effective Income Tax Rates [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	21.00%	35.00%
Reconciliation of Effective Income Tax Rates Continuing Operations
Federal income tax expense (1)	[1]	$ 17,246	$ 16,491	$ 26,249
State income taxes, net of federal benefit		5,088	4,057	2,000
ESOP dividend deduction		(173)	(158)	(257)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		0		(14,299)
Other		(1,070)	842	977
Income Tax Expense from Continuing Operations		$ 21,091	$ 21,232	$ 14,670
Effective Income Tax Rate for Continuing Operations (2)	[2]	25.65%	27.19%	19.56%

[1] Federal income taxes were calculated at 21 percent for 2019 and 2018 and 35 percent for 2017.

[2] The effective tax rate for 2017 includes the impact of the revaluation of deferred tax assets and liabilities for our unregulated businesses due to implementation of the TCJA