Commitments and Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Roll forward of activity in insurance reserves
Balance at beginning of period	$ 42,584	$ 36,967	$ 39,480
Net increases in reserves	22,938	25,139	15,686
Net payments made	(20,159)	(19,522)	(18,199)
Balance at end of period	$ 45,363	$ 42,584	$ 36,967

Amount of loss contingency liability.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

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- Definition

Amount of cash outflow reducing loss contingency liability.

+ References

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- Definition

Amount charged against operating income increasing loss contingency liability, after adjustments to reduce previously estimated charges.

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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.

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