Mergers and Acquisitions - Additional Information (Detail) - USD ($)				12 Months Ended
	Nov. 22, 2019	Aug. 20, 2018	Apr. 05, 2018	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Total Assets				$ 15,720,112,000	$ 12,458,632,000
Portfolio loans, net of unearned income				10,267,985,000	7,656,281,000
Old Line [Member]
Business Acquisition [Line Items]
Total Assets	$ 3,000,000,000.0
Portfolio loans, net of unearned income	2,500,000,000
Securities	182,520,000
Value of acquisition	$ 493,952,000
Closing stock price	$ 36.75
Number of shares issued for acquisition	13,351,837
Business acquisition, fair value	$ 3,300,000
Goodwill acquired	203,774,000			203,800,000
Purchase price allocation in core deposit intangible	33,591,000
Merger related expense				13,200,000
Cash consideration for outstanding shares	16,000
Farmers Capital Bank Corporation [Member]
Business Acquisition [Line Items]
Total Assets		$ 1,600,000,000
Portfolio loans, net of unearned income		1,000,000,000.0
Securities		239,321,000
Value of acquisition		$ 428,901,000
Closing stock price		$ 49.40
Number of shares issued for acquisition		7,920,387
Goodwill acquired		$ 223,304,000
Purchase price allocation in core deposit intangible		39,992,000
Merger related expense				3,200,000	12,400,000
Cash consideration for outstanding shares		37,634,000
First Sentry Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Total Assets			$ 704,800,000
Portfolio loans, net of unearned income			447,300,000
Securities			142,903,000
Value of acquisition			$ 108,322,000
Closing stock price			$ 42.96
Number of shares issued for acquisition			2,498,761
Goodwill acquired			$ 67,699,000
Purchase price allocation in core deposit intangible			8,078,000
Merger related expense				$ 0	$ 5,500,000
Cash consideration for outstanding shares			975,000
Community Banking [Member] | Old Line [Member]
Business Acquisition [Line Items]
Purchase price allocation in core deposit intangible	$ 33,600,000
Community Banking [Member] | Farmers Capital Bank Corporation [Member]
Business Acquisition [Line Items]
Purchase price allocation in core deposit intangible		37,400,000
Community Banking [Member] | First Sentry Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Purchase price allocation in core deposit intangible			$ 8,100,000
Trust And Investment Services [Member] | Farmers Capital Bank Corporation [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Purchase price allocation in core deposit intangible		$ 2,600,000