Office Closing and Exit Costs - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended					12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restructuring Cost And Reserve [Line Items]
Termination costs	$ 8,780	$ (77)	$ 417	$ 5,950	$ 8,371	$ 15,070	$ 8,371	$ 0
Additional accruals for severance costs						11,706	5,372
Stock-based compensation expense (gain)						217	2,999
Building lease						3,147	$ 0
Oklahoma City Restructuring
Restructuring Cost And Reserve [Line Items]
Additional accruals for severance costs						275
Stock-based compensation expense (gain)						948
Virginia and West Virginia Properties and Other
Restructuring Cost And Reserve [Line Items]
Additional accruals for severance costs						11,400
Stock-based compensation expense (gain)						$ (731)