Significant Accounting Policies (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Stock-based compensation expense	$ 942,000	$ 290,000
Operating lease right-of-use assets	65,621,000			$ 0
Operating lease liability	66,171,000
Cumulative-effect adjustment for the adoption of ASU 2016-02					$ 0
Reclassification out of property, plant and equipment	258,968,000			264,960,000
Reclassification into other assets	$ 10,293,000			7,660,000
Software | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life	5 years
Software | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life	10 years
Cloud Computing Arrangements | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life	3 years
Cloud Computing Arrangements | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life	10 years
Prepaid and other current assets
Finite-Lived Intangible Assets [Line Items]
Implementation costs	$ 300,000
Other assets
Finite-Lived Intangible Assets [Line Items]
Implementation costs	$ 2,800,000
Accounting Standards Update 2016-02
Finite-Lived Intangible Assets [Line Items]
Operating lease right-of-use assets			$ 69,000,000
Operating lease liability			69,000,000
Cumulative-effect adjustment for the adoption of ASU 2016-02				$ 0
Accounting Standards Update 2018-15
Finite-Lived Intangible Assets [Line Items]
Reclassification out of property, plant and equipment			(2,800,000)
Reclassification into other assets			$ 2,800,000