CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Operating activities:
Net income (loss)	$ (58,480)	$ 90,884
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities
Depreciation	3,233	3,073
Amortization of right-of-use operating lease assets	393	476
Amortization of patents	486	470
Amortization of premium (discount) on investments, net	1,062	(2,433)
Amortization of debt issuance costs	595	474
Amortization of convertible senior notes discount	8,834	8,726
Stock-based compensation expense	40,790	45,505
Non-cash losses related to patents, licensing and property, plant and equipment and investments	(87)	14
Provision for deferred income taxes	(3,437)	13,549
Changes in operating assets and liabilities:
Contracts receivable	34,429	4,908
Inventories	(2,181)	(2,475)
Other current and long-term assets	9,532	1,326
Accounts payable	411	(17,191)
Accrued compensation	(20,920)	(13,004)
Other current liabilities	(2,565)	13,756
Deferred contract revenue	(19,679)	(40,353)
Net cash provided by (used in) operating activities	(7,584)	107,705
Investing activities:
Purchases of short-term investments	(544,375)	(492,781)
Proceeds from sale of short-term investments	459,352	426,868
Purchases of property, plant and equipment	(9,080)	(3,229)
Acquisition of licenses and other assets, net	(904)	(1,032)
Net cash used in investing activities	(95,007)	(70,174)
Financing activities:
Proceeds from issuance of equity, net	7,652	67,057
Payments of tax withholdings related to vesting of employee stock awards and exercise of employee stock options	(11,603)	(7,597)
Repurchases and retirements of common stock	(90,550)	0	$ (34,400)
Net cash provided by financing activities	(94,501)	59,460
Net increase in cash and cash equivalents	(197,092)	96,991
Cash and cash equivalents at beginning of period	683,287	278,820	278,820
Cash and cash equivalents at end of period	486,195	375,811	$ 683,287
Supplemental disclosures of cash flow information:
Interest paid	601	667
Income taxes paid	3	0
Supplemental disclosures of non-cash investing and financing activities:
Right-of-use assets obtained in exchange for lease liabilities	0	13,557
Amounts accrued for capital and patent expenditures	$ 4,903	$ 1,864