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Employee Benefit Plans - Summary of Changes in Fair Value of Level 3 Investments (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year |  | $ 57,746 |
Balance, end of year |  | 52,250 | $ 57,746
Quoted Prices in Active Markets (Level 1) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year |  | 50,062 |
Balance, end of year |  | 46,065 | 50,062
Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year |  | 0 |
Balance, end of year |  | 0 | 0
Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year |  | 436 | 498
Purchases |  | 1,674 | 2,271
Transfers in |  | 2,375 | 1,743
Disbursements |  | (3,872) | (4,101)
Investment Income |  | 14 | 25
Balance, end of year |  | 627 | 436
Investments in equity securities |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year |  | 24,382 |
Balance, end of year |  | 20,499 | 24,382
Investments in equity securities | Quoted Prices in Active Markets (Level 1) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year |  | 24,382 |
Balance, end of year |  | 20,499 | 24,382
Investments in equity securities | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year |  | 0 |
Balance, end of year |  | 0 | 0
Investments in equity securities | Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year |  | 0 |
Balance, end of year |  | 0 | 0
Debt securities |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year |  | 21,226 |
Balance, end of year |  | 21,448 | 21,226
Debt securities | Quoted Prices in Active Markets (Level 1) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year |  | 21,226 |
Balance, end of year |  | 21,448 | 21,226
Debt securities | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year |  | 0 |
Balance, end of year |  | 0 | 0
Debt securities | Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year |  | 0 |
Balance, end of year |  | 0 | 0
Us Large Cap Equity Securities | Investments in equity securities |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [1] | 4,245 |
Balance, end of year | [1] | 3,399 | 4,245
Us Large Cap Equity Securities | Investments in equity securities | Quoted Prices in Active Markets (Level 1) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [1] | 4,245 |
Balance, end of year | [1] | 3,399 | 4,245
Us Large Cap Equity Securities | Investments in equity securities | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [1] | 0 |
Balance, end of year | [1] | 0 | 0
Us Large Cap Equity Securities | Investments in equity securities | Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [1] | 0 |
Balance, end of year | [1] | 0 | 0
Us Mid Cap Equity Securities | Investments in equity securities |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [1] | 1,775 |
Balance, end of year | [1] | 1,478 | 1,775
Us Mid Cap Equity Securities | Investments in equity securities | Quoted Prices in Active Markets (Level 1) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [1] | 1,775 |
Balance, end of year | [1] | 1,478 | 1,775
Us Mid Cap Equity Securities | Investments in equity securities | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [1] | 0 |
Balance, end of year | [1] | 0 | 0
Us Mid Cap Equity Securities | Investments in equity securities | Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [1] | 0 |
Balance, end of year | [1] | 0 | 0
United States Equity Small Cap | Investments in equity securities |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [1] | 918 |
Balance, end of year | [1] | 670 | 918
United States Equity Small Cap | Investments in equity securities | Quoted Prices in Active Markets (Level 1) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [1] | 918 |
Balance, end of year | [1] | 670 | 918
United States Equity Small Cap | Investments in equity securities | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [1] | 0 |
Balance, end of year | [1] | 0 | 0
United States Equity Small Cap | Investments in equity securities | Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [1] | 0 |
Balance, end of year | [1] | 0 | 0
International All Cap Equity | Investments in equity securities |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [2] | 11,916 |
Balance, end of year | [2] | 9,226 | 11,916
International All Cap Equity | Investments in equity securities | Quoted Prices in Active Markets (Level 1) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [2] | 11,916 |
Balance, end of year | [2] | 9,226 | 11,916
International All Cap Equity | Investments in equity securities | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [2] | 0 |
Balance, end of year | [2] | 0 | 0
International All Cap Equity | Investments in equity securities | Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [2] | 0 |
Balance, end of year | [2] | 0 | 0
Alternative Strategies | Investments in equity securities |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [3] | 5,528 |
Balance, end of year | [3] | 5,726 | 5,528
Alternative Strategies | Investments in equity securities | Quoted Prices in Active Markets (Level 1) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [3] | 5,528 |
Balance, end of year | [3] | 5,726 | 5,528
Alternative Strategies | Investments in equity securities | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [3] | 0 |
Balance, end of year | [3] | 0 | 0
Alternative Strategies | Investments in equity securities | Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [3] | 0 |
Balance, end of year | [3] | 0 | 0
High Yield Asset Backed Securities | Debt securities |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [4] | 2,772 |
Balance, end of year | [4] | 2,818 | 2,772
High Yield Asset Backed Securities | Debt securities | Quoted Prices in Active Markets (Level 1) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [4] | 2,772 |
Balance, end of year | [4] | 2,818 | 2,772
High Yield Asset Backed Securities | Debt securities | Significant Other Observable Inputs (Level 2) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [4] | 0 |
Balance, end of year | [4] | 0 | 0
High Yield Asset Backed Securities | Debt securities | Significant Unobservable Inputs (Level 3) |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |
Balance, beginning of year | [4] | 0 |
Balance, end of year | [4] | $ 0 | $ 0
[1] | Includes funds that invest primarily in United States common stocks.
[2] | Includes funds that invest primarily in foreign equities and emerging markets equities.
[3] | Includes funds that actively invest in both equity and debt securities, funds that sell short securities and funds that provide long-term capital appreciation. The funds may invest in debt securities below investment grade.
[4] | Includes funds that invest in investment grade and fixed income securities.

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- Definition Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Amount of decrease in plan assets of defined benefit plan from disposal or classification as held-for-sale. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(7) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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