Consolidated Joint Ventures (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Rig JointVenture	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
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	$ 662,829	$ 725,722	$ 512,245	$ 68,510
Bully Joint Venture
Schedule Of Equity Method Investments [Line Items]
Dividends approved and paid	113,800	171,900	$ 143,000
Carrying amount of the drillships	1,300,000	1,400,000
Cash and cash equivalents	$ 41,600	$ 34,700