Shareholders' Equity - Summary of Preferred and Common Share Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Stockholders' Equity
Issued, beginning balance	130,218,183
Treasury Stock, beginning balance	(7,848,231)
Grants of restricted stock	186,961	193,788	210,613
Vesting of performance shares	306,802	287,390	109,678
Issuance of common stock due to exercise of stock options	2,184,169	1,576,485	2,210,348
Retirement of treasury stock	3,000,000	4,000,000	17,000,000
Retirement of treasury stock	(3,000,000)	(4,000,000)	(17,000,000)
Issued, ending balance	127,218,183	130,218,183
Treasury Stock, ending balance	(9,187,075)	(7,848,231)
Preferred Stock
Increase (Decrease) in Stockholders' Equity
Issued, beginning balance	0	0	0
Treasury Stock, beginning balance	0	0	0
Issued, ending balance	0	0	0
Treasury Stock, ending balance	0	0	0
Common Stock
Increase (Decrease) in Stockholders' Equity
Issued, beginning balance	130,218,183	134,218,183.000	151,218,183
Treasury Stock, beginning balance	(7,848,231)	(6,287,907.000)	(16,965,802)
Grants of restricted stock	12,549	6,648	19,041
Forfeitures of restricted stock		$ (13,950)	$ (2,700)
Issuance of common stock due to exercise of stock options	2,184,169	1,576,485	2,210,349
Treasury stock acquired	(6,694,582)	(7,340,794)	(8,548,795)
Retirement of treasury stock	3,000,000	4,000,000	17,000,000
Retirement of treasury stock	(3,000,000)	(4,000,000)	(17,000,000)
Issued, ending balance	127,218,183.000	130,218,183	134,218,183.000
Treasury Stock, ending balance	(9,187,075.000)	(7,848,231)	(6,287,907.000)
Performance Shares
Increase (Decrease) in Stockholders' Equity
Grants of restricted stock	167,500	179,500	179,250
Performance Shares | Common Stock
Increase (Decrease) in Stockholders' Equity
Vesting of performance shares	159,020	211,287