Summary of Significant Accounting Policies - Contingent Liabilities and Commitments (Details) $ in Millions	Dec. 31, 2018 USD ($)
Accounting Policies [Abstract]
Unspent tenant related obligations	$ 47.0

Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

No definition available.

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