CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenues	$ 328,425	$ 273,718
Cost of revenues	71,153	62,477
Gross profit	257,272	211,241
Operating expenses:
Selling and marketing (excluding customer base amortization)	88,094	88,490
Software development	27,928	22,913
General and administrative	40,076	40,590
Customer base amortization	7,682	5,803
Total operating expenses	163,780	157,796
Income from operations	93,492	53,445
Interest and other income	4,945	2,987
Interest and other expense	(732)	(690)
Income before income taxes	97,705	55,742
Income tax expense	12,536	3,511
Net income	$ 85,169	$ 52,231
Net income per share-basic (in dollars per share)	$ 2.35	$ 1.46
Net income per share-diluted (in dollars per share)	$ 2.33	$ 1.44
Weighted average outstanding shares-basic (in shares)	36,237	35,893
Weighted average outstanding shares-diluted (in shares)	36,567	36,350