Pension Assets by Component (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plans-fair value of plan assets	$ 273,056	$ 258,067
Percent of total pension assets	100.00%	100.00%
Corporate Debt
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plans-fair value of plan assets	158,293	159,759
Percent of total pension assets	58.10%	61.90%
Other Fixed Maturities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plans-fair value of plan assets	340	348
Percent of total pension assets	0.10%	0.10%
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plans-fair value of plan assets	89,698	79,459
Percent of total pension assets	32.80%	30.80%
Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plans-fair value of plan assets	10,385	3,767
Percent of total pension assets	3.80%	1.50%
Guaranteed Annuity Contract
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plans-fair value of plan assets	12,633	12,745
Percent of total pension assets	4.60%	4.90%
Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plans-fair value of plan assets	$ 1,707	$ 1,989
Percent of total pension assets	0.60%	0.80%