MARKETABLE SECURITIES (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended |
Sep. 30, 2019 | Dec. 31, 2018 |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Current | $ 111,402 | $ 199,937 |
Minimum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Probabilityof Payment | 75.00% | |
Maximum [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Probabilityof Payment | 100.00% | |
Municipal Bonds [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale | $ 34,869 | 17,570 |
Corporate Debt Securities [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale | 242,684 | 246,215 |
Commercial Paper [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale | 41,227 | 50,194 |
Asset-backed Securities [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale | 157,815 | 140,181 |
Government, federal agency, and other sovereign obligations [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale | $ 17,907 | $ 8,894 |
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 | 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 | 2 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 | 3 years |
Fair Value, Measurements, Recurring [Member] | Short-term Investments [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost | $ 111,187 | $ 200,210 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 220 | 3 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (5) | (276) |
Debt Securities, Available-for-sale | | 199,937 |
Debt Securities, Available-for-sale, Current | 111,402 | |
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 | 4,665 | 14,923 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 24 | |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | | (25) |
Debt Securities, Available-for-sale | 4,689 | 14,898 |
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 | 50,539 | 118,823 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 188 | |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | | (185) |
Debt Securities, Available-for-sale | 50,727 | 118,638 |
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 | 41,229 | 50,202 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 3 | 3 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (5) | (11) |
Debt Securities, Available-for-sale | 41,227 | 50,194 |
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 | 4,760 | 11,765 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 4 | |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 0 | (54) |
Debt Securities, Available-for-sale | 4,764 | 11,711 |
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 | 9,994 | 4,497 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 1 | |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | | (1) |
Debt Securities, Available-for-sale | 9,995 | 4,496 |
Fair Value, Measurements, Recurring [Member] | Other Long-term Investments [Member] | | |
Debt Securities, Available-for-sale [Line Items] | | |
Debt Securities, Available-for-sale, Amortized Cost | 378,266 | 263,060 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 4,857 | 458 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (24) | (401) |
Debt Securities, Available-for-sale | 383,099 | 263,117 |
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 | 29,935 | 2,676 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 246 | |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (1) | (4) |
Debt Securities, Available-for-sale | 30,180 | 2,672 |
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 | 189,283 | 127,676 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 2,673 | 196 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | | (295) |
Debt Securities, Available-for-sale | 191,956 | 127,577 |
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 | 151,206 | 128,297 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 1,868 | 262 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | (23) | (89) |
Debt Securities, Available-for-sale | 153,051 | 128,470 |
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 | 7,842 | 4,411 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 70 | |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | | (13) |
Debt Securities, Available-for-sale | $ 7,912 | $ 4,398 |