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Accounting Pronouncements (Details) - USD ($) $ in Thousands | 9 Months Ended
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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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