Fair Value of Pension Plan Assets by Asset Category (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	32,776		28,471
Pension Benefits | Fair Value, Inputs, Level 1
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	1,030		702
Pension Benefits | Fair Value, Inputs, Level 2
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	31,746		27,769
Asset And Mortgage-Backed Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Percentage of fixed income fund in asset and other securities	32.00%		34.00%
US Treasury Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Percentage of fixed income fund in asset and other securities	41.00%		41.00%
Corporate Debt Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Percentage of fixed income fund in asset and other securities	27.00%		25.00%
Fixed Income Securities
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	12,582	[1]	11,062	[2]
Fixed Income Securities | Pension Benefits | Fair Value, Inputs, Level 2
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	12,582	[1]	11,062	[2]
U.S. Equity Growth
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	8,014		6,945
U.S. Equity Growth | Pension Benefits | Fair Value, Inputs, Level 2
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	8,014		6,945
U.S. Equity Value
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	8,005		6,952
U.S. Equity Value | Pension Benefits | Fair Value, Inputs, Level 2
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	8,005		6,952
Foreign Equity
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	3,145		2,810
Foreign Equity | Pension Benefits | Fair Value, Inputs, Level 2
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	3,145		2,810
Money Market Funds
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	1,030		702
Money Market Funds | Pension Benefits | Fair Value, Inputs, Level 1
Fair Value Hierarchy Of Plan Assets By Category [Line Items]
Pension plan assets	1,030		702

[1] As of December 31, 2012, the fixed income fund consisted of a 32% investment in asset and mortgage-backed securities, a 41% investment in U.S. treasury securities, and a 27% investment in corporate bonds.

[2] As of December 31, 2011, the fixed income fund consisted of a 34% investment in asset and mortgage-backed securities, a 41% investment in U.S. treasury securities, and a 25% investment in corporate bonds.