Schedule of Gain on Disposition of Assets (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2016 USD ($) Vessel	Mar. 31, 2015 USD ($) Vessel	Mar. 31, 2014 USD ($) Vessel
Impaired Assets to be Disposed of by Method Other than Sale [Line Items]
Gain on vessels disposed	$ 6,692	$ 5,883	$ 6,111	$ 7,351	$ 10,704	$ 4,699	$ 4,500	$ 3,893	$ 26,037	$ 23,796	$ 21,063
Number of vessels disposed | Vessel									17	13	48
Vessels
Impaired Assets to be Disposed of by Method Other than Sale [Line Items]
Gain on vessels disposed									$ 3,252	$ 2,988	$ 12,247