Reconciliation of Level 3 Assets (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	$ 14,768	$ 17,166
Net realized and unrealized gains (losses)	338	1,012
Net purchases, issuances and settlements	4,901	(3,410)
Net transfers into (out of) level 3
Ending balance	20,007	14,768
Other Investments
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	12,991	14,427
Net realized and unrealized gains (losses)	251	678
Net purchases, issuances and settlements	5,767	(2,114)
Net transfers into (out of) level 3
Ending balance	19,009	12,991
Fixed Income Investments
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	1,777	2,739
Net realized and unrealized gains (losses)	87	334
Net purchases, issuances and settlements	(866)	(1,296)
Net transfers into (out of) level 3
Ending balance	$ 998	$ 1,777