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Employee Benefit Plans - Additional Information (Detail) NOK in Millions |  | 1 Months Ended | 2 Months Ended | 3 Months Ended | 4 Months Ended | 6 Months Ended |
--- | --- | --- | --- | --- | --- | --- | ---
Jul. 31, 2017 USD ($) | Apr. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | Sep. 30, 2016 USD ($) | Jul. 31, 2017 USD ($) | Jul. 31, 2017 NOK | Sep. 30, 2017 USD ($) | Sep. 30, 2016 USD ($) | Sep. 30, 2016 NOK | Dec. 31, 2017 USD ($)
Pension Plans, Defined Benefit |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Defined benefit plan, employer contributions |  |  | $ 0 | $ 3,000,000 |  |  |  | $ 3,000,000 |  |
Expected contribution to the plan during the remaining quarters of fiscal 2018 |  |  | 0 |  |  |  | $ 0 |  |  |
Pension Plans, Defined Benefit | Predecessor |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Defined benefit plan, employer contributions |  |  |  |  | $ 0 |  |  |  |  |
Supplemental Executive Retirement Plan |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Defined benefit plan, employer contributions |  |  | 100,000 | $ 100,000 |  |  |  | 100,000 |  |
Expected contribution to the plan during the remaining quarters of fiscal 2018 |  |  | $ 0 |  |  |  | $ 0 |  |  |
Retirement benefit plan, description |  |  |  |  |  |  | In 1991, the company adopted a Supplemental Executive Retirement Plan (“SERP”) for certain employees. The SERP provides for retirement benefits payable in the form of a joint and survivor annuity, equivalent installments, or a lump sum. In general, the SERP provides pension benefits determined based on the average of the participant’s highest compensation for any consecutive five year period during the ten years immediately preceding retirement multiplied by the participant’s benefit service. |  |  |
Supplemental Executive Retirement Plan | Predecessor |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Defined benefit plan, employer contributions |  |  |  |  | 0 |  |  |  |  |
Supplemental Executive Retirement Plan | Scenario, Forecast |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Settlement of distribution |  | $ 9,600,000 |  |  |  |  |  |  |  |
Settlement loss |  | $ 500,000 |  |  |  |  |  |  |  |
Norway’s Defined Benefit Pension Plan |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Defined benefit plan, employer contributions | $ 0 |  |  |  | $ 400,000 | NOK 3.0 |  | $ 500,000 | NOK 3.4 |
Norway’s Defined Benefit Pension Plan | Scenario, Forecast |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Expected contribution to the plan during the remaining quarters of fiscal 2018 |  |  |  |  |  |  |  |  |  | $ 0

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- Definition Description of nature and type of retirement benefits. Includes, but is not limited to, plan utilized, employee group covered, type of plan formula and funding policy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=77993564&loc=d3e4179-114921 + Details
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