Benefit Plans - Stock Options Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Shares outstanding at beginning of year (in shares)	732,489	1,383,365	1,828,591
Shares granted (in shares)	0	0	100,000
Shares forfeited or expired (in shares)	(285,509)	(650,876)	(545,226)
Shares outstanding at end of year (in shares)	446,980	732,489	1,383,365
Shares exercisable at year-end (in shares)	446,980	632,489	1,283,365
Weighted Average Exercise Price
Weighted average exercise price, outstanding at beginning of year (in usd per share)	$ 14	$ 16	$ 17
Weighted average exercise price, granted (in usd per share)	0	0	11
Weighted average exercise price, forfeited or expired (in usd per share)	16	18	18
Weighted average exercise price, outstanding at end of year (in usd per share)	13	14	16
Weighted average exercise price, exercisable at year-end (in usd per share)	$ 13	$ 14	$ 16