Fair Value Measurements - Non-recurring measurement (Details 4) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Measurements, Nonrecurring \| Level 3
Carrying amounts and estimated fair values of the financial instruments
Limited partnership interests	$ 0	$ 9,242,000

Fair value portion of investments accounted under the cost method.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 325

-SubTopic 20

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=29638263&loc=d3e39828-111592

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