Benefit Plans - Status of Unexercised Stock Options (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options, Outstanding at beginning of year	4,248,898	4,178,764	4,101,499
Number of stock options, Granted	93,802	83,422	213,782
Number of stock options, Exercised	(2,000)	(500)	(4,174)
Number of stock options, Forfeited	(109,655)	(2,847)	(3,047)
Number of stock options, Expired	(65,308)	(9,941)	(129,296)
Number of stock options, Outstanding at the end of year	4,165,737	4,248,898	4,178,764
Weighted average exercise price, Outstanding at beginning of year	$ 17.37	$ 17.42	$ 17.81
Weighted average exercise price, Granted	$ 14.86	$ 14.50	$ 10.34
Weighted average exercise price, Exercised	$ 12.54	$ 12.54	$ 12.45
Weighted average exercise price, Forfeited	$ 10.41	$ 12.65	$ 13.26
Weighted average exercise price, Expired	$ 18.32	$ 15.85	$ 18.51
Weighted average exercise price, Outstanding at the end of year	$ 17.49	$ 17.37	$ 17.42