Pension Plans' Investments at Fair Value Represented 5% or More of Pension Plans' Net Assets (Detail) (Pension Plans, Defined Benefit, USD $)	Dec. 31, 2011	Dec. 31, 2010
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Concentration of risk investments at fair value	$ 336,287,000	$ 349,455,000
Collective Trust High Yield Fund
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Concentration of risk investments at fair value	0	21,956,000
EB Daily Valued Large Cap Growth Stock Index Fund
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Concentration of risk investments at fair value	0	18,497,000
EB Daily Valued Large Cap Value Stock Index Fund
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Concentration of risk investments at fair value	0	19,605,000
EB Daily Valued Small Cap Stock Index Fund
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Concentration of risk investments at fair value	23,038,000	34,069,000
EB Daily Valued Stock Index Fund
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Concentration of risk investments at fair value	82,060,000	110,030,000
EB Daily Valued International Stock Index Fund
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Concentration of risk investments at fair value	21,938,000	33,967,000
EB Long Term Government Bond Index
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Concentration of risk investments at fair value	44,058,000	0
EB Long Term Credit Bond Index
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Concentration of risk investments at fair value	60,111,000	21,765,000
US Treasury Securities
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Concentration of risk investments at fair value	0	11,799,000
US Government Agencies Debt Securities
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Concentration of risk investments at fair value	0	20,700,000
Corporate Debt Securities
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Concentration of risk investments at fair value	$ 105,082,000	$ 57,067,000