MARKETABLE SECURITIES (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |
Mar. 31, 2020 | Dec. 31, 2019 |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Current | $ 110,211 | $ 115,763 |
Municipal Bonds [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale | 53,240 | 53,118 |
Corporate Debt Securities [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale | 233,209 | 258,264 |
Commercial Paper [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale | 21,388 | 34,752 |
Asset-backed Securities [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale | 169,932 | 166,711 |
Government, federal agency, and other sovereign obligations [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale | $ 12,503 | $ 12,432 |
Short-term Investments [Member] | Municipal Bonds [Member] | Maximum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 1 year | 1 year |
Short-term Investments [Member] | Corporate Debt Securities [Member] | Maximum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 1 year | 1 year |
Short-term Investments [Member] | Commercial Paper [Member] | Maximum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 1 year | 1 year |
Short-term Investments [Member] | Asset-backed Securities [Member] | Maximum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 1 year | 1 year |
Short-term Investments [Member] | Government, federal agency, and other sovereign obligations [Member] | Maximum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 1 year | |
Other Long-term Investments [Member] | Municipal Bonds [Member] | Minimum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 1 year | 1 year |
Other Long-term Investments [Member] | Municipal Bonds [Member] | Maximum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 3 years | 3 years |
Other Long-term Investments [Member] | Corporate Debt Securities [Member] | Minimum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 1 year | 1 year |
Other Long-term Investments [Member] | Corporate Debt Securities [Member] | Maximum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 3 years | 3 years |
Other Long-term Investments [Member] | Asset-backed Securities [Member] | Minimum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 1 year | 1 year |
Other Long-term Investments [Member] | Asset-backed Securities [Member] | Maximum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 3 years | 3 years |
Other Long-term Investments [Member] | Government, federal agency, and other sovereign obligations [Member] | Minimum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 1 year | 1 year |
Other Long-term Investments [Member] | Government, federal agency, and other sovereign obligations [Member] | Maximum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Contractual Maturity | 2 years | 2 years |
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost, Total | $ 110,376 | $ 115,486 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 310 | 282 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (475) | (5) |
Debt Securities, Available-for-sale | 110,211 | 115,763 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Municipal Bonds [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost, Total | 12,809 | 7,840 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 63 | 23 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | | (1) |
Debt Securities, Available-for-sale | 12,872 | 7,862 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Corporate Debt Securities [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost, Total | 63,683 | 69,091 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 222 | 247 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (381) | (3) |
Debt Securities, Available-for-sale | 63,524 | 69,335 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Commercial Paper [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost, Total | 21,374 | 34,747 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 18 | 6 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (4) | (1) |
Debt Securities, Available-for-sale | 21,388 | 34,752 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Asset-backed Securities [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost, Total | 8,044 | 3,808 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 7 | 6 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (90) | |
Debt Securities, Available-for-sale | 7,961 | 3,814 |
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | Government, federal agency, and other sovereign obligations [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost, Total | 4,466 | |
Debt Securities, Available-for-sale | 4,466 | |
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost, Total | 380,219 | 405,079 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 2,210 | 4,481 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (2,368) | (46) |
Debt Securities, Available-for-sale | 380,061 | 409,514 |
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Municipal Bonds [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost, Total | 40,033 | 45,010 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 336 | 254 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | | (8) |
Debt Securities, Available-for-sale | 40,369 | 45,256 |
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Corporate Debt Securities [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost, Total | 170,419 | 186,356 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 885 | 2,578 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (1,619) | (5) |
Debt Securities, Available-for-sale | 169,685 | 188,929 |
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Asset-backed Securities [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost, Total | 161,862 | 161,347 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 857 | 1,583 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (749) | (33) |
Debt Securities, Available-for-sale | 161,970 | 162,897 |
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | Government, federal agency, and other sovereign obligations [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost, Total | 7,905 | 12,366 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 132 | 66 |
Debt Securities, Available-for-sale | $ 8,037 | $ 12,432 |