CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
OPERATING ACTIVITIES:
Net income	$ 90,415	$ 57,373
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	20,777	15,246
Stock-based compensation	73,751	56,368
Allowance for credit losses on accounts receivable	2,722	1,647
Noncash lease expense	24,052	15,394
Deferred income taxes	(20,978)
Other	1,242	(2,945)
Changes in operating assets and liabilities:
Accounts receivable	21,063	(2,739)
Prepaid expenses and other assets	(23,919)	(19,024)
Accounts payable	47,728	(21,401)
Accrued expenses and other liabilities	11,006	(3,178)
Operating lease liabilities	(10,388)	(8,468)
Net cash provided by operating activities	237,471	88,273
INVESTING ACTIVITIES:
Purchases of investments	(127,117)	(178,179)
Maturities of investments	128,315	55,819
Purchases of property and equipment	(57,721)	(21,659)
Capitalized software development costs	(4,246)	(3,849)
Net cash used in investing activities	(60,769)	(147,868)
FINANCING ACTIVITIES:
Proceeds from line of credit	143,000
Repayment on line of credit	(71,000)
Payment of debt financing costs		(6)
Proceeds from exercise of stock options	53,942	21,911
Proceeds from employee stock purchase plan	15,035	8,648
Taxes paid related to net settlement of restricted stock awards	(14,184)	(4,744)
Net cash provided by financing activities	126,793	25,809
Increase (decrease) in cash and cash equivalents	303,495	(33,786)
Cash and cash equivalents—Beginning of period	130,876	207,232
Cash and cash equivalents—End of period	434,371	173,446
SUPPLEMENTAL CASH FLOW INFORMATION:
Capitalized assets financed by accounts payable	12,842	1,968
Asset retirement obligation	1,601	3,543
Stock-based compensation included in capitalized software development costs	1,394	1,269
Cash paid for amounts included in the measurement of lease liabilities included in operating cash flows	17,702	12,268
Right-of-use assets obtained in exchange for operating lease liabilities	$ 52,238	$ 147,682