Income Taxes (Detail) - The income tax effects of temporary differences that comprise deferred tax assets and liabilities (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current deferred tax assets:
Gross current deferred tax asset	$ 1,499	$ 1,983
Less valuation allowance	(537)	(1,464)
Net current deferred tax asset	962	519
Noncurrent deferred tax assets (liabilities)
Gross non-current deferred tax assets (liabilities)	2,088	11,841
Less valuation allowance	(3,050)	(12,360)
Net noncurrent deferred tax assets (liabilities)	(962)	(519)
Property, Plant and Equipment, Other Types [Member]
Noncurrent deferred tax assets (liabilities)
Gross non-current deferred tax assets (liabilities)	(6,211)	(4,829)
Employee Benefits [Member]
Noncurrent deferred tax assets (liabilities)
Gross non-current deferred tax assets (liabilities)	3,377	3,188
Other Noncurrent Assets [Member]
Noncurrent deferred tax assets (liabilities)
Gross non-current deferred tax assets (liabilities)	142	154
AMT Credit [Member]
Noncurrent deferred tax assets (liabilities)
Gross non-current deferred tax assets (liabilities)	649	211
Net Operating Loss [Member]
Noncurrent deferred tax assets (liabilities)
Gross non-current deferred tax assets (liabilities)	4,131	13,117
Accounts Receivable [Member]
Current deferred tax assets:
Gross current deferred tax asset	243	402
Employee Benefits [Member]
Current deferred tax assets:
Gross current deferred tax asset	978	1,324
Other Accrued Expenses [Member]
Current deferred tax assets:
Gross current deferred tax asset	$ 278	$ 257