Fair value measurements - Fair value of other financial instruments not recorded at fair value (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Estimated fair values of financial instruments (other than derivative financial instruments)
Carrying amount - Loans from banks and other parties	$ 603,333	$ 620,106
Level 3
Estimated fair values of financial instruments (other than derivative financial instruments)
Fair value - Loans from banks and other parties	$ 663,845	$ 663,653

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

No definition available.

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant