CASH AND CASH EQUIVALENTS, AND SHORT-TERM INVESTMENTS (Details 2) $ in Thousands	Dec. 31, 2018 USD ($)
Cost	$ 385,272
Accretion	1,141
Gross Unrealized Gains	40
Gross Unrealized Losses	(82)
Fair Value	386,371
US treasury securities [Member]
Cost	264,619
Accretion	813
Gross Unrealized Gains	19
Gross Unrealized Losses	(58)
Fair Value	265,393
US Government agency securities [Member]
Cost	120,653
Accretion	328
Gross Unrealized Gains	21
Gross Unrealized Losses	(24)
Fair Value	$ 120,978

The amount of accumulated accretion on available for sale securities.

No definition available.

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Namespace Prefix:	iova_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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- Definition

Amount before tax of unrealized 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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Period Type:	instant

- Details

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- Details

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