Shareholders' Equity - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Capitalization, Equity [Line Items]
Retirement of treasury stock	3,000,000	3,000,000	4,000,000
Dividends paid by subsidiaries to parent company	$ 454,000	$ 438,000	$ 466,000
Maximum amount of dividends expected to be available from subsidiaries without regulatory approval during next year	315,000
Restricted net assets	940,000
Retained earnings restricted by lenders' covenants	3,500,000
Retained earnings	$ 4,806,208	$ 3,890,798
Anti-dilutive shares	0	0	0
Stock Repurchase Plan
Schedule of Capitalization, Equity [Line Items]
Shares repurchased	4,100,000	5,200,000	6,300,000
Share repurchases under stock repurchase program, amount	$ 325,000	$ 311,000	$ 359,000
Stock Repurchase Plan for Anti-Dilutive Effect
Schedule of Capitalization, Equity [Line Items]
Shares repurchased	1,100,000	1,500,000	1,000,000
Share repurchases under stock repurchase program, amount	$ 88,000	$ 93,000	$ 60,000