CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Cash Flows [Abstract]
Net income	$ 4,918	$ 904
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	4,550	3,586
Stock-based compensation	3,165	495
Provision for doubtful accounts	0	319
Deferred income taxes	280	98
Amortization of premiums on marketable securities	(13)	(71)
Other	2	(17)
Changes in operating assets and liabilities:
Accounts receivable	46,440	32,505
Prepaid expenses and other current assets	(1,241)	492
Accounts payable	(40,912)	(18,755)
Accrued expenses	(4,373)	(4,740)
Other liabilities, non-current	(129)	(121)
Net cash provided by operating activities	12,687	14,695
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(262)	(1,279)
Capitalized software development costs	(3,018)	(2,694)
Purchases of marketable securities	(23,168)	(10,498)
Proceeds from sales of marketable securities	0	2,295
Proceeds from maturities of marketable securities	9,600	12,350
Net cash (used in) provided by investing activities	(16,848)	174
CASH FLOWS FROM FINANCING ACTIVITIES:
Payments for offering costs	(805)	0
Proceeds from exercise of stock options	451	74
Payments to acquire treasury stock	(27)	0
Net cash (used in) provided by financing activities	(381)	74
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(4,542)	14,943
CASH AND CASH EQUIVALENTS - Beginning of period	81,188	34,250
CASH AND CASH EQUIVALENTS - End of period	76,646	49,193
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Income taxes paid	192	52
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Stock-based compensation capitalized as internal use software costs	153	7
Property and equipment included in accounts payable and accrued expenses	946	2,663
Capitalized software costs included in accounts payable and accrued expenses	$ 270	$ 225