Fair Value Measurements - Fair Value, by Balance Sheet Grouping (Details) - Fair Value Measurements Using Level 3 [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Carrying Amount [Member]
Liabilities
Debt, Carrying Amount	$ 1,492,483	$ 2,068,867
Fair Value [Member]
Liabilities
Debt, Fair Value	$ 1,409,773	$ 2,013,226

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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