Amount of investment in debt security measured at amortized cost (held-to-maturity).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121553693&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Name:	us-gaap_HeldToMaturitySecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Securities Available for Sale and Held to Maturity - Securities Held to Maturity by Credit Rating, as Determined by Moody's (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Securities Held to Maturity Amortized Cost	$ 611,280	$ 738,099
Aaa [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Securities Held to Maturity Amortized Cost	579,674
Aaa1 to Aa3 [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Securities Held to Maturity Amortized Cost	26,166
Not Rated [Member]
Schedule of Available For Sale and Held to Maturity Securities [Line Items]
Securities Held to Maturity Amortized Cost	$ 5,440