Securities (Other-Than-Temporary Impairment) (Details) - USD ($)	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Investment securities available-for-sale
Other Than Temporary Impairment Credit Losses Recognized in Earnings
OTTI credit losses	$ 0	$ 0

This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which no such other than temporary impairment (OTTI) was previously recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

Name:	us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsAdditionsNoPreviousImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration