Segment Information - Schedule of Selected Information for Each Business Segment (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenues from external customers	$ 85,573,000	$ 88,837,000	$ 168,203,000	$ 170,196,000
Operating income
Operating income	15,926,000	17,897,000	31,063,000	29,824,000
Interest expense	4,298,000	4,285,000	8,348,000	9,705,000
Loss on extinguishment of debt	0	0	0	2,161,000
Other income	(336,000)	(552,000)	(1,256,000)	(1,129,000)
Income before income taxes	11,964,000	14,164,000	23,971,000	19,087,000
U.S.
Segment Reporting Information [Line Items]
Revenues from external customers	74,086,000	78,100,000	145,574,000	149,127,000
Operating income
Operating income	14,292,000	16,895,000	28,448,000	28,063,000
International
Segment Reporting Information [Line Items]
Revenues from external customers	11,487,000	10,737,000	22,629,000	21,069,000
Operating income
Operating income	$ 1,634,000	$ 1,002,000	$ 2,615,000	$ 1,761,000