Leases - Sale-leaseback transaction (Details 4) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2012
Sale-leaseback transaction, deferred gain
Sale-leaseback transaction gain	$ 2,108
Sale-leaseback transaction gain, deferred		$ 4,500

The amount of the gain recorded in connection with the transaction involving the sale of property to another party and the lease of the property back to the seller to be recognized in future periods.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 40
-Section 25
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6456126&loc=d3e49567-112750

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