Summary of Costs Incurred by Individual Restructuring Action (Detail) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Restructuring charges	$ 1,553	$ 787	$ 1,623	$ 6,434
Termination benefits
Restructuring charges	1,451		1,451	867
Termination benefits | Mid-Continent Organization Restructuring
Restructuring charges			1,451
Employee and office relocation costs
Restructuring charges	102	527	172	1,202
Employee and office relocation costs | Mid-Continent Organization Restructuring
Restructuring charges			101
Employee and office relocation costs | 2009/2010 Organization Restructuring
Restructuring charges			71
Mid-Continent Organization Restructuring
Restructuring charges			1,552
2009/2010 Organization Restructuring
Restructuring charges			$ 71