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	$ (48,846)	$ (43,084)	$ (53,362)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation expense	35,804	38,436	33,731
Depreciation	3,426	3,846	3,389
Amortization of intangible assets		100	545
Accretion of premium of investment securities	(24)	(50)	(57)
Provision for doubtful accounts		199	149
Impairment of ROU assets	1,328
Loss (gain) on disposal of equipment	185	25	(16)
Changes in operating assets and liabilities:
Accounts receivable	2,179	(10,564)	(4,916)
Deferred commissions	(572)	1,078	329
Other current and noncurrent assets	(582)	(5,535)	(1,006)
Accounts payable	(775)	715	439
Unearned revenue	12,374	28,815	16,434
Customer arrangements with termination rights	(3,237)	(179)	5,348
Accrued expenses and other long-term liabilities	(3,666)	355	2,029
Net cash provided by (used in) operating activities	(2,406)	14,157	3,036
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(1,518)	(1,956)	(6,454)
Proceeds from maturities of investment securities	5,150	15,900	38,015
Purchase of investment securities	(4,126)	(10,053)	(8,570)
Net cash provided by (used in) investing activities	(494)	3,891	22,991
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from Employee Stock Purchase Plan	4,396	4,424	4,798
Proceeds from exercise of stock options	5,508	6,514	4,114
Taxes paid for net settlement of equity awards	(5,892)	(4,862)	(3,149)
Amounts withheld for net settlement of equity awards		(1,513)
Repurchases of common stock	(11,310)	(3,831)
Net cash provided by (used in) financing activities	(7,298)	732	5,763
NET CHANGE IN CASH AND CASH EQUIVALENTS	(10,198)	18,780	31,790
CASH AND CASH EQUIVALENTS—Beginning of period	104,613	85,833	54,043
CASH AND CASH EQUIVALENTS—End of period	94,415	104,613	85,833
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid for income taxes	1,813	1,419	1,189
Lease payments for amounts included in the measurement of lease liabilities	7,281	7,213	6,786
SUPPLEMENTAL DISCLOSURES OF NONCASH FINANCING ACTIVITIES:
Value of shares issued under Bonus Plans	6,374	5,898	5,123
Value of shares issued under the Employee Stock Purchase Plan	$ 4,132	4,548	4,562
Unpaid property and equipment purchases		$ 148	$ 228