Benefit Plans - Status of Unexercised Stock Options (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of stock options, outstanding at beginning of year	1,284,321	1,233,742	4,152,016
Number of stock options, granted	65,972	171,935	85,250
Number of stock options, exercised	(201,320)	(9,678)	(28,464)
Number of stock options, forfeited	(62,287)	(4,178)	(53,444)
Number of stock options, expired	(2,000)	(107,500)	(2,921,616)
Number of stock options, outstanding at the end of year	1,084,686	1,284,321	1,233,742
Weighted average exercise price, outstanding at beginning of year	$ 15.32	$ 15.24	$ 17.50
Weighted average exercise price, granted	16.38	16.44	15.23
Weighted average exercise price, exercised	15.72	12.11	12.41
Weighted average exercise price, forfeited	14.93	14.50	10.34
Weighted average exercise price, expired	17.94	16.54	18.57
Weighted average exercise price, outstanding at the end of year	$ 15.32	$ 15.32	$ 15.24