Investment Securities - Narrative (Details) $ in Millions	Sep. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Marketable Securities [Abstract]
Number of securities in unrealized loss positions for less than 12 months	24	24
Number of securities in unrealized loss position greater than 12 months	16	17
Securities pledged for deposits and borrowings \| $	$ 53.5	$ 51.6

Amount of restricted 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 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

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