Loans and reserve for credit losses (Average Recorded Investment in Impaired Financing Receivables) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 11,071	$ 12,946	$ 34,367
Commercial Real Estate Owner Occupied
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	1,757	3,216	6,115
Commercial Real Estate Non Owner Occupied
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	1,905	6,384	22,699
Commercial real estate portfolio
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	3,662	9,600	28,814
Construction portfolio
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	0	499	1,157
Residential real estate portfolio
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	0	54	381
Commercial and industrial portfolio
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	7,409	2,793	4,015
Consumer portfolio
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 0	$ 0	$ 0