Merger accounting - Calculation of Consideration Effectively Transferred (Parenthetical) (Details)		12 Months Ended
Nov. 30, 2013 $ / shares shares	Dec. 31, 2015
Business Acquisition [Line Items]
Common stock exchange ratio		1.3636
Penseco Financial Services Corp [Member]
Business Acquisition [Line Items]
Price per share \| $ / shares	$ 34.50
Common stock exchange ratio	1.3636
Common shares to be retired \| shares	9,928

Number of shares of common and preferred stock retired from treasury during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

Name:	us-gaap_TreasuryStockSharesRetired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration