Deferred revenue - Deferred Revenue (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred Revenue Disclosure [Abstract]
Deferred revenue on time charters	$ 26,879	$ 14,271
Deferred interest on lease receivable	0	1,428
Other deferred revenue	2,828	9,230
Deferred revenue	29,707	24,929
Current portion	(28,179)	(22,199)
Deferred revenue	$ 1,528	$ 2,730

The carrying amount of consideration received or receivable as of the balance sheet date on potential earnings that were not recognized as revenue in conformity with GAAP, and which are expected to be recognized as such within one year or the normal operating cycle, if longer, including sales, license fees, and royalties, but excluding interest income.

The noncurrent portion of deferred revenue amount as of balance sheet date. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized, and is not expected to be recognized in the next twelve months. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

+ References + Details