Shareholders' Equity - Summary of Preferred and Common Share Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common Stock
Issued, beginning balance	134,218,183
Retirement of treasury stock	(4,000,000)	(17,000,000)	(7,500,000)
Issued, ending balance	130,218,183	134,218,183
Treasury Stock
Treasury Stock, beginning balance	(6,287,907)
Grants of restricted stock	193,788	210,613	238,488
Vesting of performance shares	287,390	109,678	182,793
Issuance of common stock due to exercise of stock options	1,576,485	2,210,348	3,917,757
Treasury Stock, ending balance	(7,848,231)	(6,287,907)
Preferred Stock [Member]
Preferred Stock
Issued, beginning balance	0	0	0
Issued, ending balance	0	0	0
Treasury Stock
Treasury Stock, beginning balance	0	0	0
Treasury Stock, ending balance	0	0	0
Common Stock [Member]
Common Stock
Issued, beginning balance	134,218,183	151,218,183.000	158,718,183
Retirement of treasury stock	(4,000,000)	(17,000,000)	(7,500,000)
Issued, ending balance	130,218,183.000	134,218,183	151,218,183.000
Treasury Stock
Treasury Stock, beginning balance	(6,287,907)	(16,965,802.000)	(17,364,729)
Grants of restricted stock	6,648	19,041	76,415
Forfeitures and surrenders of restricted stock	$ (13,950)	$ (2,700)	$ (37,359)
Issuance of common stock due to exercise of stock options	1,576,485	2,210,349	3,917,757
Issuance of common stock due to settlement of restricted stock units			11,190
Treasury stock acquired	(7,340,794)	(8,548,795)	(11,069,076)
Retirement of treasury stock	4,000,000	17,000,000	7,500,000
Treasury Stock, ending balance	(7,848,231.000)	(6,287,907)	(16,965,802.000)
Stock Repurchase Plan [Member]
Treasury Stock
Treasury stock acquired	(6,300,000)	(7,200,000)	(8,300,000)
Performance Shares [Member]
Treasury Stock
Grants of restricted stock	179,500	179,250	147,750
Performance Shares [Member] | Common Stock [Member]
Treasury Stock
Vesting of performance shares	211,287