CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities:
Net income	$ 238,334	$ 122,695	$ 85,071
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	77,743	63,643	70,165
Amortization of deferred commissions costs	48,313	0	0
Amortization of debt issuance costs	876	2,303	3,227
Loss on extinguishment of debt	0	3,788	0
Impairment loss	0	0	23
Loss on disposal of property and equipment	73	129	839
Realized gain on investments	0	0	(808)
Stock-based compensation expense	41,214	39,030	36,349
Deferred income taxes, net	3,666	(2,903)	15,635
Bad debt expense	6,542	5,690	7,358
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	(27,819)	(17,524)	(16,044)
Prepaid expenses and other current assets	(1,651)	(3,672)	(1,157)
Deferred commissions	(53,497)	0	0
Income tax receivable	(1,927)	(12,981)	0
Accounts payable and other liabilities	(14,132)	11,525	(1,520)
Income taxes payable	9,632	16,937	2,816
Deferred revenue	7,879	6,004
Deferred revenue			(2,070)
Deposits and other assets	212	39	758
Net cash provided by operating activities	335,458	234,703	200,642
Investing activities:
Proceeds from sale and settlement of investments	0	0	5,950
Purchases of property and equipment and other assets	(29,632)	(24,499)	(18,766)
Cash paid for acquisitions, net of cash acquired	(418,369)	(47,768)	(10,443)
Net cash used in investing activities	(448,001)	(72,267)	(23,259)
Financing activities:
Payments of long-term debt	0	(345,000)	(20,000)
Payments of debt issuance costs	0	(3,467)	0
Repurchase of restricted stock to satisfy tax withholding obligations	(24,327)	(14,902)	(16,424)
Proceeds from equity offering, net of transaction costs	0	833,911	0
Proceeds from exercise of stock options and employee stock purchase plan	27,071	9,888	5,861
Net cash provided by (used in) financing activities	2,744	480,430	(30,563)
Effect of foreign currency exchange rates on cash and cash equivalents	(1,248)	1,374	(1,415)
Net (decrease) increase in cash and cash equivalents	(111,047)	644,240	145,405
Cash and cash equivalents at beginning of year	1,211,463	567,223	421,818
Cash and cash equivalents at end of year	1,100,416	1,211,463	567,223
Supplemental cash flow disclosures:
Interest paid	1,421	6,445	6,712
Income taxes paid	35,980	41,283	34,132
Supplemental non-cash investing and financing activities:
Stock issued in connection with acquisition - ForRent	36,366	0	0
Consideration owed for acquisitions	$ 1,534	$ 0	$ 0