Employee Benefit Plans - Summary of Estimated Future Benefit Payments (Detail)	Dec. 31, 2017 USD ($)
Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
2018	$ 52,237,000
Supplemental Employee Retirement Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
2018	505,169
2019	515,688
2020	511,503
2021	536,062
2022	532,639
2023-2027	$ 2,825,601

Amount of benefits for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following latest fiscal year.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in fourth fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in third fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in second fiscal year following latest fiscal year.

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