FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Money market funds | ISP Fund LP
Assets
Total assets measured at estimated fair value	$ 284,800
Equity investment | ISP Fund LP
Assets
Total assets measured at estimated fair value	14,500
Recurring basis
Assets
Total assets measured at estimated fair value	627,254	$ 306,741
Recurring basis | U.S. government securities
Assets
Total assets measured at estimated fair value		53,834
Recurring basis | U.S. commercial paper
Assets
Total assets measured at estimated fair value		18,915
Recurring basis | Money market funds
Assets
Total assets measured at estimated fair value	204,808	233,992
Recurring basis | Equity investments and Money market funds | ISP Fund LP
Assets
Total assets measured at estimated fair value	299,288
Recurring basis | Quoted Price in Active Markets for Identical Assets, Level 1
Assets
Total assets measured at estimated fair value	576,176	233,992
Recurring basis | Quoted Price in Active Markets for Identical Assets, Level 1 | U.S. government securities
Assets
Total assets measured at estimated fair value		0
Recurring basis | Quoted Price in Active Markets for Identical Assets, Level 1 | U.S. commercial paper
Assets
Total assets measured at estimated fair value		0
Recurring basis | Quoted Price in Active Markets for Identical Assets, Level 1 | Money market funds
Assets
Total assets measured at estimated fair value	204,808	233,992
Recurring basis | Quoted Price in Active Markets for Identical Assets, Level 1 | Equity investments and Money market funds | ISP Fund LP
Assets
Total assets measured at estimated fair value	299,288
Recurring basis | Significant Other Observable Inputs, Level 2
Assets
Total assets measured at estimated fair value	49,931	72,749
Recurring basis | Significant Other Observable Inputs, Level 2 | U.S. government securities
Assets
Total assets measured at estimated fair value		53,834
Recurring basis | Significant Other Observable Inputs, Level 2 | U.S. commercial paper
Assets
Total assets measured at estimated fair value		18,915
Recurring basis | Significant Other Observable Inputs, Level 2 | Money market funds
Assets
Total assets measured at estimated fair value	0	0
Recurring basis | Significant Other Observable Inputs, Level 2 | Equity investments and Money market funds | ISP Fund LP
Assets
Total assets measured at estimated fair value	0
Recurring basis | Significant Unobservable Inputs, Level 3
Assets
Total assets measured at estimated fair value	1,147	0
Recurring basis | Significant Unobservable Inputs, Level 3 | U.S. government securities
Assets
Total assets measured at estimated fair value		0
Recurring basis | Significant Unobservable Inputs, Level 3 | U.S. commercial paper
Assets
Total assets measured at estimated fair value		0
Recurring basis | Significant Unobservable Inputs, Level 3 | Money market funds
Assets
Total assets measured at estimated fair value	0	0
Recurring basis | Significant Unobservable Inputs, Level 3 | Equity investments and Money market funds | ISP Fund LP
Assets
Total assets measured at estimated fair value	0
Nonrecurring basis | Debt
Debt
2023 Notes	239,779	243,394
2025 Notes	206,135	208,976
Total fair value of debt	445,914	452,370
Nonrecurring basis | Quoted Price in Active Markets for Identical Assets, Level 1 | Debt
Debt
2023 Notes	0	0
2025 Notes	0	0
Total fair value of debt	0	0
Nonrecurring basis | Significant Other Observable Inputs, Level 2 | Debt
Debt
2023 Notes	239,779	243,394
2025 Notes	206,135	208,976
Total fair value of debt	445,914	452,370
Nonrecurring basis | Significant Unobservable Inputs, Level 3 | Debt
Debt
2023 Notes	0	0
2025 Notes	0	0
Total fair value of debt	0	$ 0
Armata | Recurring basis | Equity investment | Common stock
Assets
Total assets measured at estimated fair value	25,958
Armata | Recurring basis | Equity investment | Warrants
Assets
Total assets measured at estimated fair value	18,049
Armata | Recurring basis | Quoted Price in Active Markets for Identical Assets, Level 1 | Equity investment | Common stock
Assets
Total assets measured at estimated fair value	25,958
Armata | Recurring basis | Quoted Price in Active Markets for Identical Assets, Level 1 | Equity investment | Warrants
Assets
Total assets measured at estimated fair value	0
Armata | Recurring basis | Significant Other Observable Inputs, Level 2 | Equity investment | Common stock
Assets
Total assets measured at estimated fair value	0
Armata | Recurring basis | Significant Other Observable Inputs, Level 2 | Equity investment | Warrants
Assets
Total assets measured at estimated fair value	18,049
Armata | Recurring basis | Significant Unobservable Inputs, Level 3 | Equity investment | Common stock
Assets
Total assets measured at estimated fair value	0
Armata | Recurring basis | Significant Unobservable Inputs, Level 3 | Equity investment | Warrants
Assets
Total assets measured at estimated fair value	0
Entasis | Recurring basis | Equity investment | Common stock
Assets
Total assets measured at estimated fair value	46,122
Entasis | Recurring basis | Equity investment | Warrants
Assets
Total assets measured at estimated fair value	31,882
Entasis | Recurring basis | Quoted Price in Active Markets for Identical Assets, Level 1 | Equity investment | Common stock
Assets
Total assets measured at estimated fair value	46,122
Entasis | Recurring basis | Quoted Price in Active Markets for Identical Assets, Level 1 | Equity investment | Warrants
Assets
Total assets measured at estimated fair value	0
Entasis | Recurring basis | Significant Other Observable Inputs, Level 2 | Equity investment | Common stock
Assets
Total assets measured at estimated fair value	0
Entasis | Recurring basis | Significant Other Observable Inputs, Level 2 | Equity investment | Warrants
Assets
Total assets measured at estimated fair value	31,882
Entasis | Recurring basis | Significant Unobservable Inputs, Level 3 | Equity investment | Common stock
Assets
Total assets measured at estimated fair value	0
Entasis | Recurring basis | Significant Unobservable Inputs, Level 3 | Equity investment | Warrants
Assets
Total assets measured at estimated fair value	0
InCarda | Recurring basis | Equity investment | Warrants
Assets
Total assets measured at estimated fair value	1,147
InCarda | Recurring basis | Quoted Price in Active Markets for Identical Assets, Level 1 | Equity investment | Warrants
Assets
Total assets measured at estimated fair value	0
InCarda | Recurring basis | Significant Other Observable Inputs, Level 2 | Equity investment | Warrants
Assets
Total assets measured at estimated fair value	0
InCarda | Recurring basis | Significant Unobservable Inputs, Level 3 | Equity investment | Warrants
Assets
Total assets measured at estimated fair value	$ 1,147