Significant Accounting Policies (Schedule of Real Estate Inventory) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Inventory Disclosure [Abstract]
Completed home inventory and residential lots held for sale	$ 127,679	$ 85,342
Work in process	269,255	236,383
Undeveloped land	4,070	6,193
Land not owned under option agreements	9,293	16,214
Inventory, Real Estate	$ 410,297	$ 344,132

Inventory, Finished Homes and Land Held for Sale

No definition available.

Name:	grbk_InventoryFinishedHomesandLandHeldforSale
Namespace Prefix:	grbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of capitalized construction costs of homes for future sale and costs of land expected to be developed in the near term.

+ References

No definition available.

+ Details

Name:	grbk_InventoryHomesunderConstructionandLandunderDevelopment
Namespace Prefix:	grbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_InventoryDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The net carrying amount as of the balance sheet date of the sum of the various components of an operative builder's inventory, including finished homes. Operative builders primarily consist of entities that develop land, construct residential homes and commercial and industrial buildings thereon, and sell them to home buyers and operators of the commercial and industrial properties.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The carrying amount as of the balance sheet date of all of a real estate developer's inventories that are either not otherwise specified in the taxonomy or are not separately reported by the entity.

+ References

+ Details

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

- Definition

The carrying amount as of the balance sheet date of land not owned but under a contract in which the entity has an option to purchase the land.

+ References

+ Details

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