CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
OPERATING ACTIVITIES:
Net income	$ 57,373	$ 48,705
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	15,246	8,107
Stock-based compensation	56,368	27,958
Bad debt expense	1,647	1,727
Noncash lease expense	15,394
Other	(2,945)	2,396
Changes in operating assets and liabilities:
Accounts receivable	(2,739)	(44,736)
Prepaid expenses and other assets	(19,024)	(10,597)
Accounts payable	(21,401)	(2,804)
Accrued expenses and other liabilities	(3,178)	7,789
Operating lease liabilities	(8,468)
Net cash provided by operating activities	88,273	38,545
INVESTING ACTIVITIES:
Purchases of property and equipment	(21,659)	(10,383)
Capitalized software development costs	(3,849)	(4,340)
Purchases of investments	(178,179)
Maturities of investments	55,819
Net cash used in investing activities	(147,868)	(14,723)
FINANCING ACTIVITIES:
Repayment on line of credit		(27,000)
Payment of debt financing costs	(6)
Proceeds from exercise of stock options	21,911	7,165
Proceeds from employee stock purchase plan	8,648	7,014
Taxes paid related to net settlement of restricted stock awards	(4,744)	(602)
Net cash provided by (used in) financing activities	25,809	(13,423)
(Decrease) increase in cash and cash equivalents	(33,786)	10,399
Cash and cash equivalents—Beginning of period	207,232	155,950
Cash and cash equivalents—End of period	173,446	166,349
SUPPLEMENTAL CASH FLOW INFORMATION:
Capitalized assets financed by accounts payable	1,968	6,624
Tenant improvements paid by lessor		1,017
Asset retirement obligation	3,543	386
Stock-based compensation included in capitalized software development costs	1,269	$ 1,192
Cash paid for amounts included in the measurement of lease liabilities included in operating cash flows	12,268
Right-of-use assets obtained in exchange for operating lease liabilities	$ 147,682