Office Closing and Exit Costs - Additional Information (Detail) - USD ($)	3 Months Ended									12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost And Reserve [Line Items]
Termination costs	$ (279,000)	$ (47,000)	$ (96,000)	$ 4,192,000	$ (822,000)	$ 136,000	$ 5,000	$ 162,000	$ 8,400,000	$ 3,770,000	$ (519,000)	$ 15,070,000
Stock-based compensation expense (gain)										1,664,000	0	217,000
Building lease										(70,000)	303,000	3,147,000
Accrued severance costs										$ 2,176,000	(822,000)	11,706,000
MRD
Restructuring Cost And Reserve [Line Items]
Termination costs											0
Office closing costs											$ 0
Oklahoma City Restructuring
Restructuring Cost And Reserve [Line Items]
Additional accruals for severance costs												275,000
Stock-based compensation expense (gain)												948,000
Virginia and West Virginia Properties and Other
Restructuring Cost And Reserve [Line Items]
Additional accruals for severance costs												11,400,000
Stock-based compensation expense (gain)												$ (731,000)