Borrowed Funds - Short-Term Credit Lines Available for Use (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
FRB's Discount Window Primary Credit Program
Line of Credit Facility [Line Items]
Credit lines available for use	$ 869,724	$ 874,256
Available federal funds lines
Line of Credit Facility [Line Items]
Credit lines available for use	814,000	718,000
Correspondent bank line of credit
Line of Credit Facility [Line Items]
Credit lines available for use	$ 50,000	$ 50,000

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant