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Accounting Pronouncements (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Undistributed gains of equity method investments	$ (4,243)	$ (4,247)
Distributions in excess of current year income of equity method investments	3,210	552
Decrease (increase) in other assets	(13,881)	(6,304)
Net cash provided by operating activities	292,485	290,318
Distributions from other investments	23,420	17,041
Net cash used in investing activities	(287,356)	(277,621)
AOCI Attributable to Parent [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption	(25,019)
AOCI Attributable to Parent [Member] | Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption	(30,726)	0
AOCI Attributable to Parent [Member] | Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption	$ 5,707	0
Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Undistributed gains of equity method investments		(5,157)
Distributions in excess of current year income of equity method investments		0
Decrease (increase) in other assets		12,678
Net cash provided by operating activities		307,838
Distributions from other investments		18,503
Net cash used in investing activities		$ (276,159)

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Amount of distribution received from equity method investee for return of investment, classified as investing activities. Excludes distribution for return on investment, classified as operating activities.

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