Percentage of assets valued using observable inputs from level one or level two.

No definition available.

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- Definition

Reduced health benefit eligibility age.

+ References

No definition available.

+ Details

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- References

No definition available.

+ Details

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- Definition

The interest rate used to adjust for the time value of money for the plan.

+ 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 (k)(1)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- Definition

The interest rate used to adjust for the time value of money.

+ References

+ Details

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- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Expected Long-Term Rate of Return on Plan Assets
-URI http://asc.fasb.org/extlink&oid=6512046

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- Definition

Amount included in accumulated other comprehensive income (AOCI) related to gain (loss) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.

+ References

No definition available.

+ Details

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- Definition

Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position.

+ 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 (g)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation And Retirement Disclosure [Abstract]
Defined contribution pension plans		$ 2.7	$ 2.5	$ 2.4
CMRT
Compensation And Retirement Disclosure [Abstract]
Percentage of assets valued using observable inputs from level one or level two (or assets not subject to classification in the fair value hierarchy)		92.00%	91.00%
Defined Benefit Pension Plans
Compensation And Retirement Disclosure [Abstract]
Expected contributions to Defined Benefit Plans in Next Fiscal Year		$ 0.3
Actuarial losses expected to be recognized as a component of net period cost in next fiscal year		$ 1.6
Weighted-average rate determining the actuarial present value of benefit obligation		3.70%	4.00%
Long-term return on plan assets		7.00%	7.20%	7.20%
Weighted average discount rate, periodic benefit cost		4.00%	3.80%	4.50%
Defined Benefit Pension Plans \| CMRT
Compensation And Retirement Disclosure [Abstract]
Long-term return on plan assets		7.50%	7.50%	7.50%
OPEB
Compensation And Retirement Disclosure [Abstract]
Expected contributions to Defined Benefit Plans in Next Fiscal Year		$ 0.4
Weighted-average rate determining the actuarial present value of benefit obligation		3.10%	3.20%
Eligible age for health care benefits		65 years
Weighted average discount rate, periodic benefit cost		3.20%	3.00%	3.20%
OPEB \| Scenario Forecast
Compensation And Retirement Disclosure [Abstract]
Actuarial losses expected to be recognized as a component of net period cost in next fiscal year	$ 0.2