Derivative Instruments - Schedule of settlement of fair value hedges (Details) - Fair value hedging - Deposit liabilities - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016
Derivative [Line Items]
Cumulative reduction to interest expense	$ 119,591	$ 110,914
Remaining balance	$ 113,604	$ 122,282
Weighted average years remaining to maturity	19 years	20 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=64837297&loc=SL5624163-113959

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