Investments in affiliates (Investment affiliate rollforward) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Schedule of Equity Method Investments [Line Items]
Income (loss) from investment affiliate	$ 453	$ 2,482	$ (4,249)	$ 5,542
Investment affiliate
Schedule of Equity Method Investments [Line Items]
Balance, beginning of period	99,278	89,681	87,673	63,506
Net capital contributions	0	(4,029)	16,307	19,086
Income (loss) from investment affiliate	453	2,482	(4,249)	5,542
Balance, end of period	$ 99,731	$ 88,134	$ 99,731	$ 88,134

This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33749-111570

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

This item represents the entity's proportionate share for the period of the net income (loss) of its limited partnership investments to which the equity method of accounting is applied

+ References

No definition available.

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Limited Partnership Net Capital Contributions (Distributions)

+ References

No definition available.

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