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Employee Benefit Plans (Pension Benefit Plan) - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 37.2	$ 32.9
Estimated amortization from accumulated other comprehensive income into net periodic pension cost in 2019	0.7
Expected employer contribution to pension plan in 2019	$ 1.1
Bond Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of target allocation ranges by asset class	50.00%
Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of target allocation ranges by asset class	40.00%
Cash, Real Estate, and Managed Futures [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of target allocation ranges by asset class	10.00%
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Threshold for unamortized gain losses	10.00%

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Threshold for Recognizing Actuarial Gains Losses in Accumulated Other Comprehensive Income

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Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

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Amount included in accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan expected to be recognized in net periodic benefit (cost) credit for fiscal year following most recent annual statement of financial position.

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Amount of contributions expected to be received by defined benefit plan from employer in next fiscal year following latest fiscal year.

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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