Borrowed Funds - Summary of Borrowed Funds by Type (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 01, 2017
Debt Instrument [Line Items]
Federal Home Loan Bank advances	$ 328,465	$ 710,001
Federal funds purchased	157,975	28,000
Trust preferred borrowings	67,011	67,011
Senior debt	98,388	98,171	$ 55,000
Other borrowed funds	$ 47,949	$ 34,623
Weighted Average Interest Rate (as percent)	2.52%	1.51%
Maximum Outstanding at Month End During the Period	$ 695,484	$ 924,518
Average Amount Outstanding During the Year	$ 426,755	$ 716,962
Weighted Average Interest Rate During the Year (as percent)	1.97%	1.15%
Federal funds purchased
Debt Instrument [Line Items]
Weighted Average Interest Rate (as percent)	2.52%	1.54%
Maximum Outstanding at Month End During the Period	$ 157,975	$ 135,000
Average Amount Outstanding During the Year	$ 89,325	$ 87,438
Weighted Average Interest Rate During the Year (as percent)	1.90%	1.11%
Trust preferred borrowings
Debt Instrument [Line Items]
Weighted Average Interest Rate (as percent)	4.51%	3.25%
Maximum Outstanding at Month End During the Period	$ 67,011	$ 67,011
Average Amount Outstanding During the Year	$ 67,011	$ 67,011
Weighted Average Interest Rate During the Year (as percent)	3.84%	2.89%
Senior debt
Debt Instrument [Line Items]
Weighted Average Interest Rate (as percent)	4.50%	5.12%
Maximum Outstanding at Month End During the Period	$ 98,388	$ 155,000
Average Amount Outstanding During the Year	$ 98,275	$ 134,136
Weighted Average Interest Rate During the Year (as percent)	4.80%	4.38%
Other borrowed funds
Debt Instrument [Line Items]
Weighted Average Interest Rate (as percent)	0.23%	0.09%
Maximum Outstanding at Month End During the Period	$ 71,584	$ 97,984
Average Amount Outstanding During the Year	$ 39,314	$ 43,514
Weighted Average Interest Rate During the Year (as percent)	0.12%	0.09%