Investments in affiliates (Summary of investments in affiliates) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	$ 221,607	$ 141,243
Investment affiliate
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	39,848	34,500
Operating affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	$ 181,759	$ 106,743

Total investments in (A) an entity in which the entity has significant influence, but does not have control, (B) subsidiaries that are not required to be consolidated and are accounted for using the equity and or cost method, and (C) an entity in which the reporting entity shares control of the entity with another party or group. Includes long-term advances receivable from a party that is affiliated with the reporting entity by means of direct or indirect ownership.

Reference 1: 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

Name:	us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant