Discontinued Operations and Divestitures - Summarized Financial Information For Discontinued Operations, Net of Tax (Detail) - USD ($) $ in Thousands	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, 2017	Dec. 31, 2016	Dec. 31, 2015
Discontinued Operations And Disposal Groups [Abstract]
Revenue											$ 6,248
Loss from operations of discontinued operations before income tax expense									$ (1,092)	$ (917)	(3,518)
Income tax benefit									(437)	(375)	(1,195)
Loss from operations of discontinued operations, net of tax	$ 121	$ (206)	$ (418)	$ (152)	$ (121)	$ (133)	$ (258)	$ (30)	$ (655)	$ (542)	(2,323)
Gain on disposal of discontinued operations, before income tax expense											1,510
Income tax expense											83
Gain on disposal of discontinued operations, net of tax											$ 1,427