CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities
Net loss	$ (17,777)	$ (14,717)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	9,655	11,979
Non-cash leases expense	1,338	0
Stock-based compensation expense, net of amounts capitalized	15,111	8,540
Amortization of debt discount and issuance costs	75	242
Deferred income taxes	95	143
Gain on sale of a private company investment	(1,001)	(999)
Other	(154)	175
Changes in assets and liabilities:
Accounts receivable	163	(763)
Prepaid expenses and other assets	(2,184)	(1,857)
Accounts payable and accrued liabilities	2,991	1,099
Accrued interest on financing lease obligation, net of payments	0	(358)
Accrued compensation	(8,359)	(7,449)
Deferred revenue	9,575	9,728
Operating lease liabilities	(1,725)	0
Net cash provided by operating activities	7,803	5,763
Cash flows from investing activities
Purchases of property and equipment	(581)	(880)
Capitalized internal-use software	(3,150)	(2,640)
Proceeds from sale of a private company investment	1,001	999
Net cash used in investing activities	(2,730)	(2,521)
Cash flows from financing activities
Proceeds from stock option exercises	7,640	1
Employee payroll taxes paid for net share settlement of restricted stock units	0	(1,765)
Repayment of debt	(550)	(750)
Net cash provided by (used in) financing activities	7,090	(2,514)
Effect of exchange rate changes on cash	(44)	0
Net increase in cash, cash equivalents and restricted cash	12,119	728
Cash, cash equivalents and restricted cash at beginning of period	154,371	35,345
Cash, cash equivalents and restricted cash at end of period	166,490	36,073
Supplemental cash flow data:
Interest paid for term debt	3,423	5,126
Interest paid for financing obligation on leased facility	0	2,038
Cash paid for operating leases	3,438	0
Income taxes paid (refunds received)	247	(33)
Non-cash investing and financing transactions:
Stock compensation included in capitalized software costs	953	327
Proceeds receivable from stock option exercises	6,779	0
Accrued unpaid capital expenditures	517	1,893
Derecognized financing obligation related to building due to adoption of ASC 842	92,009	0
Derecognized building due to adoption of ASC 842	71,781	0
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents at beginning of period	153,807	35,345
Restricted cash (included in other assets) at beginning of period	$ 564	$ 0
Restricted Cash, Noncurrent Asset, Statement of Financial Position Extensible List	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Cash, cash equivalents and restricted cash at beginning of period	$ 154,371	$ 35,345
Cash and cash equivalents at end of period	165,910	36,073
Restricted cash (included in other assets) at end of period	$ 580	$ 0
Restricted Cash, Noncurrent Asset, Statement of Financial Position Extensible List	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Cash, cash equivalents and restricted cash at end of period	$ 166,490	$ 36,073