Income Taxes - Components of Income Taxes (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income tax expense from continuing operations	[1]	$ 232,645	$ 249,894	$ 256,603
Shareholders’ equity:
Other comprehensive income (loss)		186,206	(411,646)	424,089
Tax basis compensation expense (from the exercise of stock options and vesting of restricted stock awards) in excess of amounts recognized for financial reporting purposes		0	(17,577)	(18,524)
Income tax expense (benefit)		$ 418,851	$ (179,329)	$ 662,168

[1] Certain current year amounts were prospectively adjusted to give effect to the adoption of ASU 2016-09 related to excess tax benefits from stock compensation as described in Note 1—Significant Accounting Policies under "Accounting Pronouncements Adopted in the Current Year."