Quarterly Consolidated Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 86,271	$ 88,900	$ 85,573	$ 82,630	$ 81,241	$ 79,941	$ 88,837	$ 81,359	$ 343,374
Gross profit	43,845	44,885	43,846	42,309	37,899	38,527	45,947	39,762	$ 174,885	$ 162,135	$ 137,780
Net income	$ 13,293	$ 9,269	$ 9,745	$ 8,211	$ 97,126	$ 8,526	$ 13,595	$ 4,138
Basic income per weighted-average share (in dollars per share)	$ 0.35	$ 0.24	$ 0.25	$ 0.22	$ 2.58	$ 0.23	$ 0.37	$ 0.11	$ 1.06	$ 3.31	$ 0.84
Diluted income per weighted-average share (in dollars per share)	$ 0.34	$ 0.24	$ 0.25	$ 0.21	$ 2.47	$ 0.22	$ 0.35	$ 0.11	$ 1.03	$ 3.17	$ 0.82
Release valuation allowance					$ (141,100)				$ (3,969)	$ (141,094)
Impact of rate change on deferred taxes					$ 45,100				$ 0	$ 45,129	$ (383)