Debt Securities Available for Sale - Realized gains and losses on debt securities available-for-sale (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures
Gross Realized Gains	$ 41	$ 0	$ 0
Gross Realized Losses	$ 0	$ (20)	$ 0

Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27357-111563

Name:	us-gaap_DebtSecuritiesAvailableForSaleRealizedGain
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration