Asset Impairments - Additional Information (Detail) $ in Thousands		3 Months Ended				12 Months Ended
		Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) Vessel	Jun. 30, 2017 USD ($) Vessel	Jun. 30, 2016 USD ($)	Mar. 31, 2018 USD ($) Vessel	Mar. 31, 2017 USD ($)
Derivatives Fair Value [Line Items]
Asset impairments	[1]			$ 163,423	$ 36,886
Number of vessels impaired during the period				77	19
Fair value of assets incurring impairment				$ 567,975	$ 155,400
Net book value of assets				$ 2,659,314			$ 2,864,762
Stacked Vessels
Derivatives Fair Value [Line Items]
Asset impairments			$ 136,900
Number of vessels impaired during the period | Vessel			72
Fair value of assets incurring impairment			$ 504,200
Number of vessels stacked | Vessel				32
Net book value of assets				$ 190,300
Active Vessels
Derivatives Fair Value [Line Items]
Net book value of assets				$ 1,800,000
Number of vessels active | Vessel				133
Active Vessels | Scenario, Forecast
Derivatives Fair Value [Line Items]
Asset impairments						$ 26,500
Number of vessels impaired during the period | Vessel						5
Fair value of assets incurring impairment		$ 63,800

[1] Refer to Note (16) for additional information regarding asset impairment charges.