CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income	$ 58,392	$ 38,460
Adjustments to reconcile net income to net cash generated from operations:
Stock-based compensation	16,407	14,432
Deferred income taxes	10,017	5,834
Accretion of interest income	(72)	(1,053)
Depreciation and amortization of property and equipment	362	263
Non-cash amortization of right-of-use asset	749	772
Others	148	0
Changes in operating assets and liabilities:
Trade receivables	(2,797)	(2,186)
Inventory	1,414	(1,543)
Prepaid expenses and other current assets	721	1,538
Other assets	(1,088)	(100)
Accounts payable	(1,251)	(1,299)
Accrued clinical expenses	4,812	2,197
Accrued and other liabilities	(628)	(7,349)
Operating lease liabilities	(731)	(730)
Net cash provided by operating activities	86,455	49,236
Cash flows from investing activities:
Purchases of property and equipment	(89)	(667)
Proceeds from maturities of marketable securities	153,193	130,145
Purchases of marketable securities	(219,314)	(131,001)
Net cash used in investing activities	(66,210)	(1,523)
Cash flows from financing activities:
Proceeds from issuance of common stock upon exercise of options, net of issuance costs	7,347	3,947
Repurchase of common stock	(275)	(30,975)
Cash paid to satisfy statutory withholding requirement for net settlement of cashless option exercise	(63)	(4,169)
Net cash provided by (used in) financing activities	7,009	(31,197)
Net increase in cash and cash equivalents	27,254	16,516
Cash and cash equivalents, at beginning of period	31,269	41,625
Cash and cash equivalents, at end of period	58,523	58,141
Supplemental disclosure:
Exercise price of shares tendered in net settlement of cashless option exercise	772,000	931
Recognition of right-of-use asset and lease liability	$ 775,000	$ 1,878