Income Tax Expense - Schedule of Components of Effective Income Tax Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Amount
Income before income tax expense									$ 34,468	$ 30,464
U.S. federal income tax expense									7,238	6,397
Nontaxable income									(1,045)	(803)
Nondeductible expenses									45	22
Other									85	24
Income tax expense	$ 1,582	$ 1,589	$ 1,531	$ 1,621	$ 1,523	$ 1,470	$ 1,279	$ 1,368	$ 6,323	$ 5,640
Percent
Income before income tax expense (percent)									100.00%	100.00%
U.S. federal income tax expense (percent)									21.00%	21.00%
Nontaxable income (percent)									(3.00%)	(2.70%)
Nondeductible expenses (percent)									0.10%	0.10%
Other (percent)									0.20%	0.10%
Income tax expense (percent)									18.30%	18.50%