Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (4,552)	$ (221)	$ (8,969)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	14,374	10,274	8,314
Amortization of operating lease right-of-use assets	4,735
Amortization of premium on marketable investments	(1,108)	(670)	0
Provision for doubtful accounts	90	90	95
Stock-based compensation	42,065	28,484	15,343
Reversal of interest and penalties on accrued federal fees	0	0	(2,133)
Gain on sale of convertible note held for investment	(217)	(312)	0
Others	448	160	(313)
Changes in operating assets and liabilities:
Accounts receivable	(12,935)	(5,829)	(5,163)
Prepaid expenses and other current assets	(2,671)	(2,806)	(1,912)
Deferred contract acquisition costs	(12,783)	(7,748)	0
Other assets	(348)	193	(33)
Accounts payable	2,549	2,418	813
Accrued and other current liabilities	(544)	1,865	1,061
Accrued federal fees and sales tax liability	1,010	495	90
Deferred revenue	8,695	3,956	3,882
Other liabilities	(375)	392	31
Net cash provided by operating activities	51,221	38,622	11,106
Cash flows from investing activities:
Purchases of marketable investments	(359,470)	(220,704)	0
Proceeds from maturities of marketable investments	328,740	11,293	0
Purchases of property and equipment	(19,228)	(9,261)	(2,650)
Cash paid to acquire substantially all of the assets of Whendu, LLC	(13,890)	0	0
Proceeds from sale of convertible note held for investment	217	1,923	0
Net cash used in investing activities	(63,631)	(216,749)	(2,650)
Cash flows from financing activities:
Proceeds from issuance of convertible senior notes, net of issuance costs paid $8,039	0	250,711	0
Payments for capped call transactions	0	(31,412)	0
Proceeds from exercise of common stock options	7,705	7,779	6,035
Proceeds from sale of common stock under ESPP	7,823	5,730	4,101
Payments of employee taxes related to vested common stock	0	(260)	0
Repayments on revolving line of credit	0	(32,594)	0
Repayments of notes payable	0	(318)	(699)
Payments of finance leases	(7,054)	(8,544)	(7,068)
Net cash provided by financing activities	8,474	191,092	2,369
Net increase (decrease) in cash and cash equivalents	(3,936)	12,965	10,825
Cash and cash equivalents:
Beginning of year	81,912	68,947	58,122
End of year	77,976	81,912	68,947
Supplemental disclosures of cash flow data:
Cash paid for interest	1,029	2,288	3,311
Cash paid for income taxes	281	159	121
Non-cash investing and financing activities:
Equipment obtained under finance lease	0	5,142	10,261
Equipment purchased and unpaid at period-end	2,890	1,583	145
Capitalization of leasehold improvement through non-cash lease incentive	79	0	142
Acquisition and related transaction costs accrued at period-end	1,895	0	0
Convertible debt
Adjustments to reconcile net loss to net cash provided by operating activities:
Amortization of debt discount and issuance costs	$ 12,788	$ 7,881	$ 0