CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 94,181,000	$ 75,410,000	$ 129,122,000
Adjustments to reconcile net income to net cash provided by operations:
Stock-based compensation	29,313,000	23,747,000	13,361,000
Accretion of interest (income) expense	(1,738,000)	(1,721,000)	456,000
Depreciation and amortization of property and equipment	0	0	14,000
Amortization of debt financing costs	16,877,000	14,067,000	(76,703,000)
Deferred income taxes	0	0	293,000
Excess tax benefits from stock option activity	703,000	236,000	106,000
Amortization of right-of-use asset	1,468,000
Changes in operating assets and liabilities:
Trade receivables	(2,340,000)	(2,288,000)	(5,440,000)
Other receivable	0	12,896,000	(12,896,000)
Inventory	(1,044,000)	(7,779,000)	(2,262,000)
Prepaid expenses and other current assets	1,696,000	(5,071,000)	(705,000)
Other assets	(3,398,000)	0	(26,000)
Accounts payable	(735,000)	(389,000)	6,289,000
Accrued clinical expenses	2,956,000	1,274,000	780,000
Accrued and other liabilities	(517,000)	5,044,000	8,546,000
Long-term accrued income taxes	147,000	239,000	0
Operating lease liability	(1,452,000)	0	0
Net cash provided by operating activities	136,117,000	115,665,000	60,935,000
Cash flows from investing activities:
Purchases of property and equipment	(1,088,000)	(298,000)	(419,000)
Proceeds from maturities of marketable securities	182,295,000	142,655,000	29,950,000
Purchases of marketable securities	(299,035,000)	(233,124,000)	(102,987,000)
Net cash used in investing activities	(117,828,000)	(90,767,000)	(73,456,000)
Cash flows from financing activities:
Proceeds from exercise of stock options, net of issuance costs	8,419,000	9,322,000	7,181,000
Repurchase of common stock	(30,975,000)	(23,657,000)	0
Payments related to debt obligation	0	0	(15,134,000)
Cash paid to satisfy statutory withholding requirement for the net settlement of cashless option exercise	(6,089,000)
Net cash used in financing activities	(28,645,000)	(14,335,000)	(7,953,000)
Net increase (decrease) in cash and cash equivalents	(10,356,000)	10,563,000	(20,474,000)
Cash and cash equivalents, at beginning of period	41,625,000	31,062,000	51,536,000
Cash and cash equivalents, at end of period	31,269,000	41,625,000	31,062,000
Supplemental disclosure:
Income taxes paid	6,744,000	1,351,000	377,000
Cost of shares repurchased for net settlement of cashless option exercise	1,983,000	$ 0	$ 0
Recognition of right-of-use asset and lease liability	$ 4,913,000