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FAIR VALUE MEASUREMENTS - Available-for-Sale Investments Included in Cash Equivalents (Details) - Cash and Cash Equivalents - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Adjusted Cost | $ 85,993 | $ 85,363
Gross Unrealized Losses | (16) | (33)
Fair Value | 85,977 | 85,330
Municipal bonds and notes |  |
Debt Securities, Available-for-sale [Line Items] |  |
Adjusted Cost | 4,188 | 12,149
Gross Unrealized Losses | 0 | (7)
Fair Value | 4,188 | 12,142
Corporate debt securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Adjusted Cost | 48,535 | 51,862
Gross Unrealized Losses | (16) | (26)
Fair Value | 48,519 | 51,836
Financial institution instruments |  |
Debt Securities, Available-for-sale [Line Items] |  |
Adjusted Cost | 33,270 | 21,352
Gross Unrealized Losses | 0 | 0
Fair Value | $ 33,270 | $ 21,352

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- Definition Amount before tax of unrealized gain (loss) in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References No definition available. + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
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