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Significant Accounting Policies [Line Items]

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Additions made to capitalized computer software costs during the period.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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Amount before valuation and LIFO reserves of raw materials expected to be sold, or consumed within one year or operating cycle, if longer.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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Amount of restructuring charges, remediation cost, and asset impairment loss.

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Carrying value as of the balance sheet date of obligations and payables pertaining to claims incurred of a workers compensation nature.

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Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Significant Accounting Policies [Line Items]
Materials Valued At Cost	$ 11,900	$ 5,000
Restructuring gains	(2,411)	(1,925)	$ (6,003)
Cash and cash equivalents	233,711	189,326	252,836	$ 255,961
Capitalized Computer Software, Additions	7,900	6,600	2,300
Minimum [Member]
Significant Accounting Policies [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	15,000
Workers' Compensation Liability	500
Maximum [Member]
Significant Accounting Policies [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	18,000
Workers' Compensation Liability	$ 1,000
Software Development [Member] \| Minimum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Software Development [Member] \| Maximum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	7 years
3531 Construction Machinery and Equip [Member] \| Minimum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	3 years
3531 Construction Machinery and Equip [Member] \| Maximum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Other Capitalized Property Plant and Equipment [Member] \| Minimum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Other Capitalized Property Plant and Equipment [Member] \| Maximum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Consolidated Construction Joint Venture [Member] \| Joint Venture Consolidated [Member]
Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 94,359	$ 73,115
Noncontrolling Interest [Member] \| Enterprise Improvement Plan [Member] \| Restructuring Type, Real Estate Asset Impairment [Member]
Significant Accounting Policies [Line Items]
Restructuring and impairment gains - non-controlling interest			$ 3,300
Workers Compensation and Public Liability [Member]
Significant Accounting Policies [Line Items]
Change in Loss Assumptions, Potential Effect on Operating Results and Financial Position	1,000
Health Insurance Product Line [Member]
Significant Accounting Policies [Line Items]
Change in Loss Assumptions, Potential Effect on Operating Results and Financial Position	$ 300