Employee Benefits - Additional Information (Detail) - USD ($) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Bank-Owned Life Insurance [Member] | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Cash surrender value | $ 48,300,000 | ||
| Bank-Owned Life Insurance [Member] | Central Bancorp, Inc [Member] | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Cash surrender value | $ 18,300,000 | ||
| 401(k) Plan [Member] | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Percent of participant contributions | 75.00% | ||
| Percent of employer contribution (up to) | 8.00% | ||
| Contributions | $ 1,600,000 | $ 1,300,000 | $ 1,000,000 |
| Deferred compensation plan [Member] | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Liabilities for the deferred compensation plan and interest | $ 0 | $ 0 | |
| X | ||||||||||
- Definition Carrying amount as of the balance sheet date of amounts which could be received based on the terms of the insurance contract upon surrendering life policies owned by the entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition The carrying amount of the liability as of the balance sheet date to an individual under a deferred compensation arrangement. This amount may be the result of periodic accruals made over the period of active employment, or reflect termination benefits resulting contractual terms or a death benefit. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Definition The amount of the cost recognized during the period for defined contribution plans. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. No definition available.
|
| X | ||||||||||
- Definition Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan. No definition available.
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|