Benefit Plans - Change in Projected Benefit Obligation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	$ 176,339		$ 145,034
Interest cost	6,889		6,897		$ 6,645
Actuarial (gain) loss	(17,177)		28,749
Benefits paid	(8,390)		(4,341)
Projected benefit obligation at end of year	157,661		176,339		145,034
Change in fair value of plan assets:
Fair value of plan assets at beginning of year	194,646	[1]	184,910
Actual return on plan assets	2,875		13,813
Employer contributions	283		264
Benefits paid	(8,390)		(4,341)
Fair value of plan assets at end of year	189,414	[1]	194,646	[1]	$ 184,910
Funded status of the plan	31,753		18,307
Asset recognized	31,753		18,307
Accumulated benefit obligation	157,661		176,339
Accrued interest receivable	$ 607		$ 652

[1] Includes accrued interest receivable of $607 thousand and $652 thousand as of December 31, 2015 and 2014, respectively.