Employee Benefit Plans - Summary of Benefit Obligations and Funded Status of the Plan (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation at end of year	$ 157,328,000	$ 142,980,000
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	153,960,000	128,758,000
Service cost	2,283,000	2,248,000	$ 2,835,000
Interest cost	4,507,000	5,266,000	4,517,000
Actuarial loss	14,376,000	22,395,000
Plan amendment	(313,000)
Benefits paid	(6,380,000)	(4,707,000)
Projected benefit obligation at end of year	168,433,000	153,960,000	128,758,000
Change in fair value of plan assets:
Fair value of plan assets at beginning of year	167,720,000	141,108,000
Actual return on plan assets	24,376,000	28,319,000
Employer contribution	0	3,000,000	2,500,000
Benefits paid	(6,380,000)	(4,707,000)
Fair value of plan assets at end of year	185,716,000	167,720,000	141,108,000
Amounts recognized in the statement of financial position:
Funded status	17,284,000	13,760,000
Net amounts recognized as receivable pension costs in the consolidated balance sheets	17,284,000	13,760,000
Amounts recognized in accumulated other comprehensive income consist of:
Unrecognized prior service (credit) cost	(227,000)	52,000
Unrecognized net loss	21,726,000	24,486,000
Net amounts recognized in accumulated other comprehensive income (before tax)	$ 21,499,000	$ 24,538,000
Weighted average assumptions used to determine benefit obligations:
Discount rate	2.74%	3.38%
Rate of compensation increase	3.30%	3.53%
Expected long-term return on assets	6.11%	6.30%
Farmers Capital Bank Corporation Postretirement Medical Benefit Plan [Member]
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	$ 12,632,000	$ 11,514,000
Interest cost	360,000	460,000
Actuarial loss	302,000	1,304,000
Participant contributions	353,000	392,000
Benefits paid	(952,000)	(1,038,000)
Projected benefit obligation at end of year	12,695,000	12,632,000	$ 11,514,000
Amounts recognized in the statement of financial position:
Funded status	(12,695,000)	(12,632,000)
Net amounts recognized as receivable pension costs in the consolidated balance sheets	(12,695,000)	(12,632,000)
Amounts recognized in accumulated other comprehensive income consist of:
Unrecognized prior service (credit) cost	(2,792,000)	(3,016,000)
Unrecognized net loss	(1,388,000)	(1,153,000)
Net amounts recognized in accumulated other comprehensive income (before tax)	$ (1,404,000)	$ (1,863,000)
Weighted average assumptions used to determine benefit obligations:
Discount rate	2.65%	3.35%