Employee Benefit Plans (Company's Benefit Obligations, Assets and Funded Status) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in projected benefit obligation:
Service costs	$ 1,560	$ 1,315	$ 1,915
Interest costs	27,744	29,180	26,861
Change in plan assets:
Fair value of plan assets at beginning of year	339,365
Fair value of plan assets at end of year	329,987	339,365
Defined Benefit Pension Plans
Change in projected benefit obligation:
Benefit obligation at beginning of year	450,667	382,035
Interest costs	17,537	18,644
Plan amendment	(4,775)
Actuarial (gains) losses	(25,583)	76,164
Benefits paid	(21,430)	(26,176)
Projected benefit obligation at end of year	416,416	450,667	382,035
Change in plan assets:
Fair value of plan assets at beginning of year	339,365	313,469
Actual (losses) returns on plan assets	(9,620)	24,400
Contributions	21,672	27,672
Benefits paid	(21,430)	(26,176)
Fair value of plan assets at end of year	329,987	339,365	313,469
Reconciliation of funded status, Unfunded status of the plans	(86,429)	(111,302)
Amounts recognized in the consolidated balance sheet, Accrued benefit liability	(86,429)	(111,302)
Unrecognized net actuarial loss	202,087	219,081
Unrecognized prior service (credit) cost	(4,775)	15
Amounts recognized in accumulated other comprehensive income	197,312	219,096
Accumulated benefit obligation at end of year	416,416	450,667
Unfunded Supplemental Benefit Plans
Change in projected benefit obligation:
Benefit obligation at beginning of year	262,137	226,458
Service costs	1,560	1,315
Interest costs	10,207	10,536
Actuarial (gains) losses	(11,835)	37,281
Benefits paid	(13,409)	(13,453)
Projected benefit obligation at end of year	248,660	262,137	$ 226,458
Change in plan assets:
Contributions	13,409	13,453
Benefits paid	(13,409)	(13,453)
Reconciliation of funded status, Unfunded status of the plans	(248,660)	(262,137)
Amounts recognized in the consolidated balance sheet, Accrued benefit liability	(248,660)	(262,137)
Unrecognized net actuarial loss	99,023	120,642
Unrecognized prior service (credit) cost	(20,785)	(24,964)
Amounts recognized in accumulated other comprehensive income	78,238	95,678
Accumulated benefit obligation at end of year	$ 248,660	$ 262,137