Note 6 - Fair Value Measurements - Amortized Cost and Estimated Fair Value of Available-for-sale Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Homebuilding Segment [Member] \| Cash and Cash Equivalents [Member]
Amortized Cost	$ 34,882	$ 99,663
OTTI
Net Amortized Cost	34,882	99,663
Debt securities (available-for-sale)	$ 34,882	99,663
Homebuilding Segment [Member] \| Marketable Securities [Member]
Amortized Cost		49,634
OTTI
Net Amortized Cost		49,634
Debt securities (available-for-sale)		49,634
Financial Services Segment [Member] \| Cash and Cash Equivalents [Member]
Amortized Cost		200
OTTI
Net Amortized Cost		200
Debt securities (available-for-sale)		$ 200

The accumulated amount by which the fair value of an investment in debt securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary.

No definition available.

+ Details

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

- Definition

This item represents the cost of debt securities before any impairment adjustment, which are categorized neither as held-to-maturity nor trading.

+ References

No definition available.

+ Details

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

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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

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- Details

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- Details

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- Details

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