Income Taxes - Components of Income from Continuing Operations before Income Taxes and Noncontrolling Shareholders' Interests (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income From Continuing Operations Before Income Taxes And Noncontrolling Shareholders Interests [Line Items]
Income from continuing operations before income taxes and noncontrolling shareholders' interests	$ 38,809	$ 94,584	$ 68,122	$ 42,410	$ 99,982	$ 74,236	$ 106,005	$ 86,870	$ 243,925	$ 367,093	$ 334,028
United States
Income From Continuing Operations Before Income Taxes And Noncontrolling Shareholders Interests [Line Items]
Income from continuing operations before income taxes and noncontrolling shareholders' interests									211,225	319,156	314,263
Foreign
Income From Continuing Operations Before Income Taxes And Noncontrolling Shareholders Interests [Line Items]
Income from continuing operations before income taxes and noncontrolling shareholders' interests									$ 32,700	$ 47,937	$ 19,765