CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
OPERATING ACTIVITIES:
Net income	$ 24,057	$ 10,151
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	6,477	4,456
Stock-based compensation	22,965	15,869
Allowance for credit losses on accounts receivable	1,310	224
Investment credit loss	275
Noncash lease expense	7,402	4,421
Other	3,209	379
Changes in operating assets and liabilities:
Accounts receivable	210,552	127,232
Prepaid expenses and other assets	(15,791)	(6,580)
Accounts payable	(205,967)	(138,886)
Accrued expenses and other liabilities	892	(4,489)
Operating lease liabilities	(2,673)	(3,066)
Net cash provided by operating activities	52,708	9,711
INVESTING ACTIVITIES:
Purchases of investments	(35,705)	(73,950)
Maturities of investments	39,180
Purchases of property and equipment	(18,310)	(6,085)
Capitalized software development costs	(965)	(1,417)
Net cash used in investing activities	(15,800)	(81,452)
FINANCING ACTIVITIES:
Proceeds from line of credit	143,000
Payment of debt financing costs		(6)
Proceeds from exercise of stock options	19,320	9,502
Taxes paid related to net settlement of restricted stock awards	(4,893)	(1,146)
Net cash provided by financing activities	157,427	8,350
Increase (decrease) in cash and cash equivalents	194,335	(63,391)
Cash and cash equivalents—Beginning of period	130,876	207,232
Cash and cash equivalents—End of period	325,211	143,841
SUPPLEMENTAL CASH FLOW INFORMATION:
Capitalized assets financed by accounts payable	10,200	1,487
Asset retirement obligation	65	126
Stock-based compensation included in capitalized software development costs	298	455
Cash paid for amounts included in the measurement of lease liabilities included in operating cash flows	4,902	3,792
Right-of-use assets obtained in exchange for operating lease liabilities	$ 34,155	$ 35,015