Loans receivable (Details 5) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Composition of impaired loans by portfolio segment and by class of financing receivable
Nonaccrual loans 90 or more days delinquent	$ 32,913	$ 41,326
Nonaccrual loans less than 90 days delinquent	40,394	38,482
Loans less than 90 days delinquent reviewed for impairment	30,414	31,666
TDRs less than 90 days delinquent not included elsewhere	28,984	25,705
Total impaired loans	132,705	137,179
Average recorded investment in impaired loans	139,916	159,638
Interest income recognized on impaired loans	1,420	5,871
Personal Banking
Composition of impaired loans by portfolio segment and by class of financing receivable
Nonaccrual loans 90 or more days delinquent	22,759	26,752
Nonaccrual loans less than 90 days delinquent	7,297	6,831
TDRs less than 90 days delinquent not included elsewhere	7,691	7,551
Total impaired loans	37,747	41,134
Average recorded investment in impaired loans	39,162	42,363
Interest income recognized on impaired loans	363	1,368
Personal Banking | Residential mortgage loans
Composition of impaired loans by portfolio segment and by class of financing receivable
Nonaccrual loans 90 or more days delinquent	15,068	17,696
Nonaccrual loans less than 90 days delinquent	4,165	3,498
TDRs less than 90 days delinquent not included elsewhere	5,931	5,845
Total impaired loans	25,164	27,039
Average recorded investment in impaired loans	25,316	28,227
Interest income recognized on impaired loans	218	817
Personal Banking | Home equity loans
Composition of impaired loans by portfolio segment and by class of financing receivable
Nonaccrual loans 90 or more days delinquent	5,646	6,606
Nonaccrual loans less than 90 days delinquent	2,797	2,963
TDRs less than 90 days delinquent not included elsewhere	1,760	1,706
Total impaired loans	10,203	11,275
Average recorded investment in impaired loans	11,124	11,753
Interest income recognized on impaired loans	121	485
Personal Banking | Other consumer loans
Composition of impaired loans by portfolio segment and by class of financing receivable
Nonaccrual loans 90 or more days delinquent	2,045	2,450
Nonaccrual loans less than 90 days delinquent	335	370
Total impaired loans	2,380	2,820
Average recorded investment in impaired loans	2,722	2,383
Interest income recognized on impaired loans	24	66
Business Banking
Composition of impaired loans by portfolio segment and by class of financing receivable
Nonaccrual loans 90 or more days delinquent	10,154	14,574
Nonaccrual loans less than 90 days delinquent	33,097	31,651
Loans less than 90 days delinquent reviewed for impairment	30,414	31,666
TDRs less than 90 days delinquent not included elsewhere	21,293	18,154
Total impaired loans	94,958	96,045
Average recorded investment in impaired loans	100,754	117,275
Interest income recognized on impaired loans	1,057	4,503
Business Banking | Commercial real estate loans
Composition of impaired loans by portfolio segment and by class of financing receivable
Nonaccrual loans 90 or more days delinquent	8,233	11,099
Nonaccrual loans less than 90 days delinquent	23,417	27,548
Loans less than 90 days delinquent reviewed for impairment	25,367	26,400
TDRs less than 90 days delinquent not included elsewhere	17,628	12,128
Total impaired loans	74,645	77,175
Average recorded investment in impaired loans	80,773	90,187
Interest income recognized on impaired loans	846	3,589
Business Banking | Commercial loans
Composition of impaired loans by portfolio segment and by class of financing receivable
Nonaccrual loans 90 or more days delinquent	1,921	3,475
Nonaccrual loans less than 90 days delinquent	9,680	4,103
Loans less than 90 days delinquent reviewed for impairment	5,047	5,266
TDRs less than 90 days delinquent not included elsewhere	3,665	6,026
Total impaired loans	20,313	18,870
Average recorded investment in impaired loans	19,981	27,088
Interest income recognized on impaired loans	$ 211	$ 914