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Amount of benefits from a defined benefit plan expected to be paid in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Target allocation maximum percentage of investments of this type to total plan assets presented on a weighted average basis.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)(i)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 5

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-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920

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Target allocation minimum percentage of investments of this type to total plan assets presented on a weighted average basis.

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Transfers in and out of Level 3. For example, transfers due to changes in the observability of significant inputs.

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-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)(iv)(02)(C)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920

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Amount of discretionary contributions made by an employer to a defined contribution plan.

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No definition available.

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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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Maximum amount the employee may contribute to a defined contribution plan.

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Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

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Employee Benefits - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Benefits expected to be paid in 2015	$ 1,212,000
Benefits expected to be paid in 2016	1,277,000
Benefits expected to be paid in 2017	1,361,000
Benefits expected to be paid in 2018	1,398,000
Benefits expected to be paid in 2019	1,456,000
Aggregate benefits expected to paid	9,124,000
Discretionary bonus expense	1,434,000	1,313,000	1,289,000
Transfers in or out of level3	0	0
Voluntary contribution of employees	33.30%
Contributions matched by compensation contribution	6.00%
Voluntary contribution of employees, amount	346,000	322,000	308,000
Supplemental Insurance/ Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits expected to be paid in 2015	1,110,000
Benefits expected to be paid in 2016	1,544,000
Benefits expected to be paid in 2017	2,004,000
Benefits expected to be paid in 2018	2,012,000
Benefits expected to be paid in 2019	2,037,000
Aggregate benefits expected to paid	11,144,000
Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Discretionary bonus expense				$ 1,000,000
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation mix for the common and collective trust portfolio, Minimum	40.00%
Allocation mix for the common and collective trust portfolio, Maximum	64.00%
Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation mix for the common and collective trust portfolio, Minimum	15.00%
Allocation mix for the common and collective trust portfolio, Maximum	25.00%
Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation mix for the common and collective trust portfolio, Minimum	20.00%
Allocation mix for the common and collective trust portfolio, Maximum	36.00%