Significant Accounting Policies (Liabilities) (Details) $ in Millions	12 Months Ended
Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)
Significant Accounting Policies
Contract liability \| $	$ 44.8	$ 62.8
Number of delivery contracts with specified volume \| item	1

Cumulative provision for contract losses not offset against related costs accumulated on the balance sheet.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 35
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=51671739&loc=d3e57777-111642

Name:	us-gaap_ProvisionForLossOnContracts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant