CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income	$ 80,017	$ 64,800
Adjustments to reconcile net income to net cash generated from operations:
Stock-based compensation	25,109	21,703
Deferred income taxes	11,778	11,731
Amortization (accretion) of interest income		(1,413)
Amortization (accretion) of interest income	404
Depreciation and amortization of property and equipment	447	474
Non-cash amortization of right-of-use asset	1,228	1,136
Others	148	0
Changes in operating assets and liabilities:
Trade receivables	(2,029)	(4,817)
Inventory	694	(654)
Prepaid expenses and other current assets	(1,882)	(58)
Other assets	(1,562)	(100)
Accounts payable	(988)	(2,424)
Accrued clinical expenses	9,055	600
Accrued and other liabilities	(4,315)	(2,207)
Operating lease liabilities	(1,205)	(1,108)
Net cash provided by operating activities	116,899	87,663
Cash flows from investing activities:
Purchases of property and equipment	(807)	(953)
Proceeds from maturities of marketable securities	193,418	168,445
Purchases of marketable securities	(323,094)	(223,331)
Net cash used in investing activities	(130,483)	(55,839)
Cash flows from financing activities:
Proceeds from issuance of common stock upon exercise of options, net of issuance costs	13,240	6,643
Repurchase of common stock	(275)	(30,975)
Cash paid to satisfy statutory withholding requirement for net settlement of cashless option exercise	(90)	(4,169)
Net cash provided by (used in) financing activities	12,875	(28,501)
Net (decrease) increase in cash and cash equivalents	(709)	3,323
Cash and cash equivalents, at beginning of period	31,269	41,625
Cash and cash equivalents, at end of period	30,560	44,948
Supplemental disclosure:
Exercise price of shares tendered in net settlement of cashless option exercise	900	931
Recognition of right-of-use asset and lease liability	$ 775	$ 1,878