CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenues	$ 1,191,832	$ 965,230	$ 837,630
Cost of Goods and Services Sold	269,933	220,403	173,814
Gross profit	921,899	744,827	663,816
Operating expenses:
Selling and marketing (excluding customer base amortization)	359,858	318,362	296,483
Software development	100,937	88,850	76,400
General and administrative	156,659	146,128	123,297
Customer base amortization	30,881	17,671	22,731
Total operating expenses	648,335	571,011	518,911
Income from operations	273,564	173,816	144,905
Interest and other income	13,281	4,044	1,773
Interest and other expense	(2,830)	(9,014)	(10,016)
Loss on debt extinguishment	0	(3,788)	0
Income before income taxes	284,015	165,058	136,662
Income tax expense	45,681	42,363	51,591
Net income	$ 238,334	$ 122,695	$ 85,071
Net income (loss) per share — basic (in dollars per share)	$ 6.61	$ 3.70	$ 2.64
Net income (loss) per share — diluted (in dollars per share)	$ 6.54	$ 3.66	$ 2.62
Weighted average outstanding shares — basic (in shares)	36,058	33,200	32,167
Weighted average outstanding shares — diluted (in shares)	36,448	33,559	32,436