Derivative Instruments - Schedule of settlement of fair value hedges (Details) - Fair value hedging - Deposit liabilities - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Derivative [Line Items]
Cumulative reduction to interest expense	$ 125,935	$ 117,818
Remaining balance	$ 107,260	$ 115,377
Weighted average years remaining to maturity	18 years	19 years 4 months 24 days

Fair value of all derivative liabilities designated as fair value hedging instruments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

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