Employee Benefit Plans - Components of and Weighted-Average Assumptions Used in Determining Net Periodic Benefit Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of net periodic benefit cost:
Service cost—benefits earned during year	$ 2,248	$ 2,835	$ 2,578
Interest cost on projected benefit obligation	5,266	4,517	4,393
Expected return on plan assets	(8,869)	(8,939)	(7,647)
Amortization of prior service cost	26	26	26
Amortization of net loss	3,240	3,053	3,221
Net periodic pension cost	1,911	1,492	2,571
Interest cost	5,266	4,517	4,393
Amortization of prior service cost	(3,042)	(2,948)	(3,247)
Net periodic pension cost	1,911	1,492	2,571
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net loss (gain) for period	2,946	2,068	(300)
Unrecognized loss on merged plan		1,429
Amortization of prior service cost	(26)	(26)	(26)
Amortization of net loss	(3,240)	(3,053)	(3,221)
Total recognized in other comprehensive income	(320)	418	(3,547)
Total recognized in net periodic pension cost and other comprehensive income	1,591	1,910	(976)
Net (gain) loss for the period	(2,946)	(2,068)	300
Amortization of prior service cost	26	26	26
Total recognized in other comprehensive income	$ (320)	$ 418	$ (3,547)
Weighted-average assumptions used to determine net periodic pension cost:
Discount rate	4.48%	3.81%	4.46%
Rate of compensation increase	3.62%	3.70%	3.74%
Expected long-term return on assets	6.30%	6.30%	6.30%
Farmers Capital Bank Corporation Postretirement Medical Benefit Plan [Member]
Components of net periodic benefit cost:
Interest cost on projected benefit obligation	$ 460	$ 138
Net periodic pension cost	236	17
Interest cost	460	138
Amortization of prior service cost	(224)	(121)
Net periodic pension cost	236	17
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net loss (gain) for period	(1,304)	151
Amortization of prior service cost	(224)	(121)
Total recognized in other comprehensive income	1,528	2,105
Total recognized in net periodic pension cost and other comprehensive income	1,764	2,122
Prior service cost for period		2,135
Net (gain) loss for the period	1,304	(151)
Amortization of prior service cost	224	121
Total recognized in other comprehensive income	$ 1,528	$ 2,105
Weighted-average assumptions used to determine net periodic pension cost:
Discount rate	2.96%	4.05%