Note 13 - Stock-based Compensation - Assumptions Valuation for Market Value Stock Units (Details) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) $ / shares shares
Dividend yield	0.00%
Market Value Stock Units [Member]
Total target shares (in shares) \| shares	336,000
Fair value per share (in dollars per share) \| $ / shares	$ 55.81
Total amount to be recognized over the service period \| $	$ 18,752
Risk free interest rate	2.29%
Expected volatility	47.52%
Dividend yield

The total mount of compensation expenses are expected to be recognized over the performance period.

No definition available.

Name:	iphi_CompensationExpensesRecognizedOverPerformancePeriod
Namespace Prefix:	iphi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the estimated fair value per share of the Company's stock related to share-based payment award.

+ References

No definition available.

+ Details

Name:	iphi_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsEstimatedFairValue
Namespace Prefix:	iphi_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of shares are expected to issue during the performance period.

+ References

No definition available.

+ Details

Name:	iphi_TargetShares
Namespace Prefix:	iphi_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iii)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(ii)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iv)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=iphi_MarketValueStockUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: