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Benefit plans (Narrative) (Details) (USD $)
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12 Months Ended |
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Dec. 31, 2014
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Dec. 31, 2013
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Dec. 31, 2012
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| Benefit Plans [Line Items] |
|
|
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| Defined Contribution Plan, Vesting Period |
5 years |
|
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| Contributions to 401(k) profit sharing plan |
$ 700,000 |
$ 500,000 |
$ 500,000 |
| Bank owned life insurance |
53,449,000 |
36,567,000 |
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| Deferred Compensation, Excluding Share-based Payments and Retirement Benefits |
|
|
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| Benefit Plans [Line Items] |
|
|
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| Other post-retirement defined benefit plan, liabilities |
7,400,000 |
3,900,000 |
|
| Deferred compensation arrangement, individual, compensation expense |
300,000 |
100,000 |
200,000 |
| Supplemental Employee Retirement Plan |
|
|
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| Benefit Plans [Line Items] |
|
|
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| Other post-retirement defined benefit plan, liabilities |
18,700,000 |
12,700,000 |
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| Deferred compensation arrangement, individual, compensation expense |
1,000,000 |
800,000 |
(500,000) |
| General Account BOLI |
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|
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| Benefit Plans [Line Items] |
|
|
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| Bank owned life insurance |
25,100,000 |
8,700,000 |
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| Separate Account BOLI |
|
|
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| Benefit Plans [Line Items] |
|
|
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| Bank owned life insurance |
$ 28,300,000 |
$ 27,900,000 |
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