Subsequent Events - Additional Information (Detail) - USD ($)				3 Months Ended		6 Months Ended
	Aug. 02, 2017	Apr. 26, 2017	Feb. 15, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Aug. 04, 2017
Subsequent Event [Line Items]
Quarterly cash dividend declared (in dollars per share)		$ 2.00	$ 2.00	$ 2	$ 1.75	$ 4	$ 3.5
Subsequent event [Member]
Subsequent Event [Line Items]
Quarterly cash dividend declared (in dollars per share)	$ 2.00
Equity offering agreement, authorized amount								$ 750,000,000.0