Other accrued liabilities - Schedule of Other Accrued Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Current:
Employee benefits	$ 19,267	$ 16,549
Self insurance	5,965	6,686
Environmental	165	240
Other	5,472	5,886
Total	30,869	29,361
Noncurrent:
Workers compensation payments	1,503	1,243
Environmental	140	165
Other	576	483
Total	$ 2,219	$ 1,891