Employee Benefit Plans - Tax Effect on Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Amounts in Accumulated Other Comprehensive Loss Expected to be Recognized in Net Periodic Benefit Costs
Net actuarial loss	$ (9.5)	$ (9.3)
Deferred tax benefit	$ 2.1

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from pension benefits.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32621-109319

Name:	us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant