Changes in Level Three Fixed Income Instrument Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value of plan assets at end of year	$ 611,284	$ 644,931
Fixed Income
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value of plan assets at end of year	479,529	516,428
Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value of plan assets at end of year	3,769	1,576
Level 3 | Fixed Income
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value of plan assets at beginning of year	1,576
Purchases, net	2,120	1,532
Total unrealized gains	73	44
Fair value of plan assets at end of year	$ 3,769	$ 1,576