Summary of Significant Accounting Policies - Accounts Receivable (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Miscellaneous receivables	$ 0.8	$ 0.7

Amount, after allowance, of receivables classified as other, due within one year or the operating cycle, if longer.

No definition available.

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