CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
REVENUE	$ 696,957	$ 545,451	$ 462,609
COSTS AND EXPENSES:
Cost of revenue	321,210	256,994	224,581
Marketing	198,949	152,387	124,209
General and administrative	78,305	68,290	64,651
Depreciation and amortization	15,082	13,736	9,158
Total costs and expenses	613,546	491,407	422,599
Operating income	83,411	54,044	40,010
INTEREST (INCOME) EXPENSE, net	(119)	26	169
Income before income tax expense	83,530	54,018	39,841
INCOME TAX EXPENSE	25,658	18,549	13,698
Net income	$ 57,872	$ 35,469	$ 26,143
BASIC INCOME PER COMMON SHARE	$ 1.93	$ 1.20	$ 0.90
DILUTED INCOME PER COMMON SHARE	$ 1.90	$ 1.19	$ 0.89
WEIGHTED AVERAGE SHARES OUTSTANDING:
Basic	29,706	29,213	28,695
Diluted	30,191	29,545	29,175
DIVIDENDS DECLARED PER COMMON SHARE	$ 0.70	$ 0.70	$ 0.70