Significant Accounting Policies (Details 1) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2013 Number
Collateralized Debt Obligations Number of Securities	9
Collateralized Debt Obligations Bonds Face Value	$ 352,533
Collateralized Debt Obligations Bonds Amortized Cost	7,462
Collateralized Debt Obligations Bonds Gross Unrealized Gain	183
Collateralized Debt Obligations Bonds Other Than Temporary Impairment	(1,682)
Collateralized Debt Obligations Bonds Fair Value	7,645
Collateralized Debt Obligations Bonds Weighted Average Expected Life	6 years
Held-to-maturity Securities [Member]
Collateralized Debt Obligations Number of Securities	9
Collateralized Debt Obligations Bonds Face Value	352,533
Collateralized Debt Obligations Bonds Amortized Cost	7,462
Collateralized Debt Obligations Bonds Gross Unrealized Gain	183
Collateralized Debt Obligations Bonds Other Than Temporary Impairment	(1,682)
Collateralized Debt Obligations Bonds Fair Value	$ 7,645
Collateralized Debt Obligations Bonds Weighted Average Expected Life	6 years

Represents amortized cost of the collateralized debt obligation bonds.

No definition available.

Name:	gkk_CollateralizedDebtObligationsBondsAmortizedCost
Namespace Prefix:	gkk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the face value of the collateralized debt obligation bonds as of the balance sheet date.

No definition available.

Name:	gkk_CollateralizedDebtObligationsBondsFaceValue
Namespace Prefix:	gkk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the fair value of the collateralized debt obligation bonds as of the balance sheet date.

No definition available.

Name:	gkk_CollateralizedDebtObligationsBondsFairValue
Namespace Prefix:	gkk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents gross unrealized gain of the collateralized debt obligation bonds.

No definition available.

Name:	gkk_CollateralizedDebtObligationsBondsGrossUnrealizedGain
Namespace Prefix:	gkk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents other-than-temporary impairment of the collateralized debt obligation bonds.

No definition available.

Name:	gkk_CollateralizedDebtObligationsBondsOtherThanTemporaryImpairment
Namespace Prefix:	gkk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents the weighted average expectedlife of the collateralized debt obligation bonds.

No definition available.

Name:	gkk_CollateralizedDebtObligationsBondsWeightedAverageExpectedLife
Namespace Prefix:	gkk_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Number of securites for the collateralized debt obligation.

No definition available.

Name:	gkk_CollateralizedDebtObligationsNumberofSecurities
Namespace Prefix:	gkk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant