Loans receivable (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2013	Dec. 31, 2012
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	$ 5,610,285	$ 5,702,480
Allowance for loan losses	67,982	69,193
Recorded investment in loans on nonaccrual	125,742	120,212
Recorded investment in loans past due 90 days or more and still accruing	781	1,698
TDRs	91,365	89,444
Minimum number of days past due and still accruing	90 days	90 days
Residential mortgage loans
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	2,374,384	2,415,649
Home equity loans
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	1,052,485	1,076,637
Other consumer loans
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	218,464	235,367
Commercial real estate
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	1,572,948	1,585,833
Commercial loans
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	392,004	388,994
Personal Banking
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	3,645,333	3,727,653
Allowance for loan losses	20,949	21,452
Recorded investment in loans on nonaccrual	41,460	36,177
Recorded investment in loans past due 90 days or more and still accruing	758	787
TDRs	7,324	6,936
Personal Banking \| Residential mortgage loans
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	2,374,384	2,415,649
Allowance for loan losses	7,878	8,002
Recorded investment in loans on nonaccrual	29,902	25,083
Recorded investment in loans past due 90 days or more and still accruing	8	9
TDRs	5,196	5,045
Personal Banking \| Home equity loans
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	1,052,485	1,076,637
Allowance for loan losses	8,211	8,294
Recorded investment in loans on nonaccrual	9,569	9,114
Recorded investment in loans past due 90 days or more and still accruing		2
TDRs	2,128	1,891
Personal Banking \| Other consumer loans
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	218,464	235,367
Allowance for loan losses	4,860	5,156
Recorded investment in loans on nonaccrual	1,989	1,980
Recorded investment in loans past due 90 days or more and still accruing	750	776
Business Banking
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	1,964,952	1,974,827
Allowance for loan losses	47,033	47,741
Recorded investment in loans on nonaccrual	84,282	84,035
Recorded investment in loans past due 90 days or more and still accruing	23	911
TDRs	84,041	82,508
Business Banking \| Commercial real estate
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	1,572,948	1,585,833
Allowance for loan losses	35,560	34,499
Recorded investment in loans on nonaccrual	55,018	57,861
Recorded investment in loans past due 90 days or more and still accruing		388
TDRs	50,944	49,826
Business Banking \| Commercial loans
Loan portfolio by portfolio segment and by class of financing receivable
Recorded investment in loans receivable	392,004	388,994
Allowance for loan losses	11,473	13,242
Recorded investment in loans on nonaccrual	29,264	26,174
Recorded investment in loans past due 90 days or more and still accruing	23	523
TDRs	$ 33,097	$ 32,682

Represents balance of financing receivable (by class) 90 days or more past maturity and still accruing.

No definition available.

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- Definition

The allowance for loan and lease losses represents the reserve to cover probable credit losses related to all loans and leases, as well as probable credit losses inherent in the remainder of the loan portfolio as of the balance sheet date excluding unallocated amounts.

+ References

No definition available.

+ Details

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- Details

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- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6951948&loc=d3e18845-111554

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- Definition

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5111-111524

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- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

+ Details

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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher OTS

-Name Federal Regulation (FR)

-Number Title 12

-Section 563c.102

-Paragraph 8

-Subparagraph e

-Chapter V

-Subsection I

-LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-DEP

-Paragraph 116

-IssueDate 2006-05-01

-Chapter 8

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5074-111524

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6375948&loc=d3e4428-111522

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 13

-Subparagraph e

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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