Consolidated Joint Ventures (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) Rig JointVenture	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Schedule Of Equity Method Investments [Line Items]
Percent of interest in joint ventures			50.00%
Number of joint ventures | JointVenture			2
Number of bully class drillships | Rig			2
Percentage of dividends paid to joint venture partner			50.00%
Cash and cash equivalents	$ 608,763	$ 426,052	$ 608,763	$ 426,052	$ 725,722	$ 512,245
Bully Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Dividends approved	30,900		83,500
Dividends paid	41,800	$ 41,800	52,600	$ 124,000
Carrying amount of the drillships	1,300,000		1,300,000		1,400,000
Cash and cash equivalents	$ 79,300		$ 79,300		$ 34,700