CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net income	$ 30,065	$ 18,274
Adjustments to reconcile net income to net cash generated from operations:
Stock-based compensation	7,918	6,696
Deferred income taxes	5,095	926
Accretion of interest income	(177)	(634)
Depreciation and amortization of property and equipment	238	96
Non-cash amortization of right-of-use asset	364	413
Changes in operating assets and liabilities:
Trade receivables	(6,756)	(1,630)
Inventory	1,328	910
Prepaid expenses and other current assets	351	1,999
Other assets	7	(25)
Accounts payable	(2,600)	953
Accrued clinical expenses	1,461	1,016
Accrued and other liabilities	(3,676)	(4,956)
Operating lease liabilities	(349)	(357)
Net cash provided by operating activities	33,269	23,681
Cash flows from investing activities:
Purchases of property and equipment	(42)	(257)
Proceeds from maturities of marketable securities	68,245	70,825
Purchases of marketable securities	(48,469)	(70,935)
Net cash provided by (used in) investing activities	19,734	(367)
Cash flows from financing activities:
Proceeds from issuance of common stock upon exercise of options, net of issuance costs	480	2,435
Repurchase of common stock	(275)	(13,555)
Cash paid to satisfy statutory withholding requirement for net settlement of cashless option exercise	0	(4,169)
Net cash provided by (used in) financing activities	205	(15,289)
Net increase in cash and cash equivalents	53,208	8,025
Cash and cash equivalents, at beginning of period	31,269	41,625
Cash and cash equivalents, at end of period	84,477	49,650
Supplemental disclosure:
Exercise price of shares tendered in net settlement of cashless option exercise	0	931
Recognition of right-of-use asset and lease liability	$ 0	$ 1,878