Estimated Future Benefit Payments under the Plans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Elgin Plan
Schedule of Pension and Other Postretirment Benefits Expected Benefit Payments [Line Items]
2012	$ 304
2013	309
2014	302
2015	297
2016 through 2021	1,788
Smithville Plan
Schedule of Pension and Other Postretirment Benefits Expected Benefit Payments [Line Items]
2012	409
2013	461
2014	496
2015	516
2016 through 2021	3,945
Wrexham Plan
Schedule of Pension and Other Postretirment Benefits Expected Benefit Payments [Line Items]
2012	465
2013	480
2014	496
2015	511
2016 through 2021	3,392
Directors Plans
Schedule of Pension and Other Postretirment Benefits Expected Benefit Payments [Line Items]
2016 through 2021	$ 6,865