Components Of Periodic Benefit Costs For Defined-Benefit Pension, Postretirement Healthcare And Supplemental Retirement Plan (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Defined-Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 216	$ 193	$ 431	$ 387
Interest cost	477	455	953	910
Expected return on plan assets	(509)	(513)	(1,018)	(1,026)
Amortization of net loss	470	343	943	685
Net periodic benefit cost	654	478	1,309	956
Postretirement Healthcare Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	9	18	19
Interest cost	18	21	36	41
Amortization of net loss	5	7	11	14
Net periodic benefit cost	33	37	65	74
Supplemental Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	5	15	10
Interest cost	40	40	80	80
Amortization of net loss	48	38	96	76
Net periodic benefit cost	$ 96	$ 83	$ 191	$ 166