Mergers and Acquisitions - Additional Information (Detail) $ / shares in Units, $ in Thousands			6 Months Ended
	Apr. 19, 2018 USD ($) Branch $ / shares shares	Apr. 05, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Total Assets			$ 10,946,584	$ 9,816,178
Portfolio loans, net of unearned income			6,792,899	6,341,441
Deposits			7,668,604	$ 7,043,588
First Sentry Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Total Assets		$ 706,100
Portfolio loans, net of unearned income		448,300
Securities		142,903
Value of acquisition		$ 108,322
Closing stock price | $ / shares		$ 42.96
Number of shares issued for acquisition | shares		2,498,761
Cash paid for acquisition		$ 975
Goodwill acquired		66,219
Purchase price allocation in core deposit intangible		8,237
Merger related expense			5,000
Total assets acquired		$ 772,292
Farmers Capital Bank Corporation [Member]
Business Acquisition [Line Items]
Portfolio loans, net of unearned income	$ 1,000,000
Value of acquisition	378,200
Merger related expense			$ 700
Total assets acquired	1,700,000
Deposits	$ 1,400,000
Number of branches entered into definitive agreement and plan of merger | Branch	34
Number of shares issued for each acquiree share | shares	1.053
Cash paid in excess of shares issued | $ / shares	$ 5.00
Total consideration per share | $ / shares	$ 50.31