Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Total revenues	$ 96,353	$ 89,733	$ 174,102	$ 166,927
Operating expenses:
Selling and marketing	32,709	30,508	65,720	61,130
General and administrative	10,940	10,419	21,679	20,589
Depreciation	2,095	1,489	4,091	3,168
Amortization of intangible assets	182	194	368	385
Acquisition and integration costs	329		329
Total operating expenses	85,326	79,520	165,363	153,578
Income from operations	11,027	10,213	8,739	13,349
Other income, net	271	93	153	102
Losses on investments, net	(20)	(22)	(45)	(225)
Income before income taxes	11,278	10,284	8,847	13,226
Income tax expense	3,490	4,220	2,792	4,132
Net income	$ 7,788	$ 6,064	$ 6,055	$ 9,094
Basic income per common share	$ 0.43	$ 0.34	$ 0.34	$ 0.51
Diluted income per common share	$ 0.43	$ 0.34	$ 0.33	$ 0.50
Basic weighted average common shares outstanding	17,965	17,715	18,001	17,973
Diluted weighted average common shares outstanding	18,290	18,050	18,313	18,293
Cash dividends declared per common share	$ 0.20	$ 0.19	$ 0.40	$ 0.38
Research Services [Member]
Revenues:
Total revenues	$ 58,300	$ 54,575	$ 110,000	$ 106,318
Advisory Services and Events [Member]
Revenues:
Total revenues	38,053	35,158	64,102	60,609
Cost of Services and Fulfillment [Member]
Operating expenses:
Cost of services and fulfillment	$ 39,071	$ 36,910	$ 73,176	$ 68,306