Short-term Borrowings - Summary of Short-Term Borrowings (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Ending Balance	$ 117,373	$ 201,853	$ 721,823
Average Balance	$ 142,634	$ 391,547	$ 618,957
Average Rate	0.49%	2.12%	1.74%
Federal funds purchased
Short-term Debt [Line Items]
Ending Balance	$ 0	$ 0	$ 11,000
Average Balance	$ 4,147	$ 8,069	$ 8,801
Average Rate	1.06%	2.53%	2.05%
Borrowings from FHLB
Short-term Debt [Line Items]
Ending Balance	$ 0	$ 136,200	$ 565,000
Average Balance	$ 28,252	$ 278,930	$ 467,594
Average Rate	1.54%	2.62%	2.12%
Securities sold under agreements to repurchase
Short-term Debt [Line Items]
Ending Balance	$ 117,373	$ 65,653	$ 145,823
Average Balance	$ 110,235	$ 104,548	$ 142,562
Average Rate	0.21%	0.75%	0.44%
Maximum [Member]
Short-term Debt [Line Items]
Ending Balance	$ 248,471	$ 670,831	$ 811,026
Weighted Average [Member]
Short-term Debt [Line Items]
Average Rate	0.10%	1.41%	2.17%