Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenues	$ 325,058	$ 239,741	$ 648,828	$ 472,311
Costs and expenses:
Operations and support	162,406	102,445	323,756	198,728
Sales and marketing	74,128	46,231	152,582	94,987
Technology (exclusive of amortization)	29,400	18,717	56,650	36,048
General and administrative	25,784	18,180	48,571	35,877
Depreciation and amortization	27,223	19,849	52,312	40,800
Total costs and expenses	318,941	205,422	633,871	406,440
Income from operations	6,117	34,319	14,957	65,871
Interest expense - net	5,467	8	8,279	1,030
Income before provision for income taxes	650	34,311	6,678	64,841
Income tax (benefit) expense	(602)	4,191	(1,464)	3,955
Net income attributable to common stockholders	$ 1,252	$ 30,120	$ 8,142	$ 60,886
Net income per share attributable to common stockholders
Basic	$ 0.01	$ 0.34	$ 0.09	$ 0.69
Diluted	$ 0.01	$ 0.33	$ 0.09	$ 0.67
Weighted-average shares used to compute net income per share attributable to common stockholders:
Basic	91,177	89,503	91,064	88,294
Diluted	92,786	92,503	92,852	91,297