Short-term Borrowings - Summary of Short-Term Borrowings (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Short-term Debt [Line Items]
Ending Balance	$ 201,853	$ 721,823	$ 707,466
Average Balance	$ 391,547	$ 618,957	$ 867,391
Average Rate	2.12%	1.74%	1.01%
Federal funds purchased
Short-term Debt [Line Items]
Ending Balance	$ 0	$ 11,000	$ 0
Average Balance	$ 8,069	$ 8,801	$ 6,225
Average Rate	2.53%	2.05%	1.24%
Borrowings from FHLB
Short-term Debt [Line Items]
Ending Balance	$ 136,200	$ 565,000	$ 567,500
Average Balance	$ 278,930	$ 467,594	$ 710,932
Average Rate	2.62%	2.12%	1.18%
Securities sold under agreements to repurchase
Short-term Debt [Line Items]
Ending Balance	$ 65,653	$ 145,823	$ 139,966
Average Balance	$ 104,548	$ 142,562	$ 150,234
Average Rate	0.75%	0.44%	0.24%
Maximum [Member]
Short-term Debt [Line Items]
Ending Balance	$ 670,831	$ 811,026	$ 967,259
Weighted Average [Member]
Short-term Debt [Line Items]
Average Rate	1.41%	2.17%	1.27%

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(1))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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