Employee Benefit Plans (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Expense related to benefit plans	$ 11,300	$ 10,800	$ 11,400
Net actuarial loss expected to be recognized	$ 6,200
Modeling process confidence ratio	90.00%
Percentage of equity investments in mutual fund	71.00%
Net periodic benefit cost, Expected return on plan assets	7.25%	7.25%	7.75%
Expected defined benefit plans contribution within a year	$ 4,900
Target percentage of pay at age 55	45.00%
Target percentage of pay at age 60	60.00%
Stock purchase plan expense	$ 9,660	$ 9,142	$ 8,814
Number of stock plans	3
Intrinsic value of outstanding in-the-money stock options	$ 26,200
Outstanding in-the-money exercisable stock options	$ 25,300
Weighted-average period, unrecognized expense related to stock options, years	2 years 11 months 6 days
Weighted-average period, unrecognized expense related to non-vested stock awards, years	2 years 11 months
Weighted-average fair value of stock options granted	$ 10.23	$ 16.97	$ 13.74
401(k) Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contribution match by employer	100.00%
Participants contribution eligible for match	6.00%
Stock purchase plan expense	$ 13,300	$ 12,300	$ 11,500
Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Target asset allocation percentage	65.00%
Fixed Income Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Target asset allocation percentage	32.00%
Two Thousand Fifteen Plan [Member] | Stock Options [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Life period of options awarded, years	10 years
Vesting period of options awarded, years	4 years
Two Thousand Fifteen Plan [Member] | Non Vested Stock Awards and Stock Units [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Life period of options awarded, years	10 years
Cliff vesting period, years	4 years
Two Thousand Five Plan [Member] | Stock Options [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Life period of options awarded, years		10 years	10 years
Vesting period of options awarded, years		4 years	4 years
Two Thousand Five Plan [Member] | Non Vested Stock Awards and Stock Units [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Life period of options awarded, years		10 years	10 years
Cliff vesting period, years		4 years	4 years
2007 Directors Plan [Member] | Stock Options [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Options awarded during period	0	0	0
Minimum [Member] | 401(k) Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contribution percentage of eligible compensation	2.00%
Maximum [Member] | 401(k) Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contribution percentage of eligible compensation	50.00%