Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Parent Company [Member]
Trading Securities, Change in Unrealized Holding Gain (Loss)	$ (484)	$ (842)	$ (400)	$ (1,705)
Partnership Interest [Member]
Trading Securities, Change in Unrealized Holding Gain (Loss)	$ (484)	$ (842)	$ (400)	$ (1,705)

Amount of unrealized holding gain (loss) recognized in the income statement for investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

No definition available.

Name:	us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration