Income Taxes - Summary of Reconciliation of Statutory Federal Tax and Effective Income Tax Rates (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Effective Income Tax Rates Continuing Operations
Federal income tax expense (1)	[1]	$ 16,291	$ 25,351	$ 22,759
State income taxes, net of federal benefit		4,088	1,894	3,422
ESOP dividend deduction		(158)	(257)	(264)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		0	(14,299)	0
Other		773	1,620	2,424
Total Income Tax Expense		$ 20,994	$ 14,309	$ 28,341
Effective Income Tax Rate (2)	[2]	27.06%	19.75%	38.81%

[1] Federal income taxes were calculated at 21 percent for 2018 and 35 percent for 2017 and 2016.

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