XML 42 R36.htm IDEA: XBRL DOCUMENT v2.4.1.9
Derivatives (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Derivative [Line Items]      
Derivative assets, fair value $ 5,727us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue $ 18,488us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue  
Derivative liabilities, fair value (35,898)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue (6,681)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue  
Notional amount of derivative instruments added 7,950,000dx_NotionalAmountofDerivativeInstrumentsAdded    
Notional amount of derivative instruments terminated (215,000)dx_NotionalAmountofDerivativeInstrumentsTerminated    
Derivatives, notional amount 17,525,000invest_DerivativeNotionalAmount 9,790,000invest_DerivativeNotionalAmount  
Gain (loss) on derivative instruments, net (53,393)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet (10,076)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet (908)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
Not Designated as Hedging Instrument [Member]      
Derivative [Line Items]      
Derivative assets, aggregate notional amount 440,000us-gaap_DerivativeAssetNotionalAmount
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 575,000us-gaap_DerivativeAssetNotionalAmount
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		  
Derivative liabilities, aggregate notional amount 17,085,000us-gaap_DerivativeLiabilityNotionalAmount
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 9,215,000us-gaap_DerivativeLiabilityNotionalAmount
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		  
Interest Rate Swap [Member]      
Derivative [Line Items]      
Derivative assets, fair value 5,727us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember		 18,488us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember		  
Derivative liabilities, fair value (3,002)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember		 (1,336)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember		  
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]      
Derivative [Line Items]      
Derivative assets, aggregate notional amount 440,000us-gaap_DerivativeAssetNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 575,000us-gaap_DerivativeAssetNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		  
Derivative liabilities, aggregate notional amount 485,000us-gaap_DerivativeLiabilityNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 215,000us-gaap_DerivativeLiabilityNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		  
Eurodollar Future [Member]      
Derivative [Line Items]      
Derivative assets, fair value 0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember		    
Derivative liabilities, fair value (32,896)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember		 (5,345)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember		  
Notional amount of derivative instruments added 7,600,000dx_NotionalAmountofDerivativeInstrumentsAdded
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember		    
Notional amount of derivative instruments terminated 0dx_NotionalAmountofDerivativeInstrumentsTerminated
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember		    
Derivatives, notional amount 16,600,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember		 9,000,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember		  
Gain (loss) on derivative instruments, net (27,551)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember		 (19,391)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember		 0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember
Eurodollar Future [Member] | Not Designated as Hedging Instrument [Member]      
Derivative [Line Items]      
Derivative assets, aggregate notional amount 0us-gaap_DerivativeAssetNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]    
Derivative liabilities, aggregate notional amount 16,600,000us-gaap_DerivativeLiabilityNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] 9,000,000us-gaap_DerivativeLiabilityNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_EurodollarFutureMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]  
Long [Member] | Interest Rate Swap [Member]      
Derivative [Line Items]      
Notional amount of derivative instruments added 275,000dx_NotionalAmountofDerivativeInstrumentsAdded
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Notional amount of derivative instruments terminated 0dx_NotionalAmountofDerivativeInstrumentsTerminated
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Derivatives, notional amount 275,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		 0invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		  
Gain (loss) on derivative instruments, net 4,912us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		 0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		 0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember
Long [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 37-48 Months [Member]      
Derivative [Line Items]      
Derivatives, notional amount 0invest_DerivativeNotionalAmount
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext3748MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Weighted-average Fixed Pay Rate 0.00%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext3748MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Weighted-average Fixed Receive Rate 0.00%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext3748MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Long [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 49-60 Months [Member]      
Derivative [Line Items]      
Derivatives, notional amount 250,000invest_DerivativeNotionalAmount
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext4960MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Weighted-average Fixed Pay Rate 2.00%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext4960MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Weighted-average Fixed Receive Rate 2.00%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext4960MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Long [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 61-72 Months [Member]      
Derivative [Line Items]      
Derivatives, notional amount 0invest_DerivativeNotionalAmount
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext6172MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Weighted-average Fixed Pay Rate 0.00%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext6172MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Weighted-average Fixed Receive Rate 0.00%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext6172MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Long [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 73-84 Months [Member]      
Derivative [Line Items]      
Derivatives, notional amount 0invest_DerivativeNotionalAmount
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext7384MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Weighted-average Fixed Pay Rate 0.00%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext7384MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Weighted-average Fixed Receive Rate 0.00%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext7384MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Long [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 97-108 Months [Member]      
Derivative [Line Items]      
Derivatives, notional amount 0invest_DerivativeNotionalAmount
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext97108MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Weighted-average Fixed Pay Rate 0.00%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext97108MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Weighted-average Fixed Receive Rate 0.00%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext97108MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Long [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 109-120 Months [Member]      
Derivative [Line Items]      
Derivatives, notional amount 25,000invest_DerivativeNotionalAmount
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext109120MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Weighted-average Fixed Pay Rate 3.00%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext109120MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Weighted-average Fixed Receive Rate 3.00%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext109120MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_LongMember		    
Short [Member] | Interest Rate Swap [Member]      
Derivative [Line Items]      
Notional amount of derivative instruments added 75,000dx_NotionalAmountofDerivativeInstrumentsAdded
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Notional amount of derivative instruments terminated (215,000)dx_NotionalAmountofDerivativeInstrumentsTerminated
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Derivatives, notional amount 650,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		 790,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		  
Gain (loss) on derivative instruments, net (30,754)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		 9,315us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		 (908)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember
Short [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 37-48 Months [Member]      
Derivative [Line Items]      
Derivatives, notional amount 185,000invest_DerivativeNotionalAmount
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext3748MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Weighted-average Fixed Pay Rate 0.92%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext3748MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Weighted-average Fixed Receive Rate 0.92%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext3748MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Short [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 49-60 Months [Member]      
Derivative [Line Items]      
Derivatives, notional amount 235,000invest_DerivativeNotionalAmount
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext4960MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Weighted-average Fixed Pay Rate 1.45%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext4960MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Weighted-average Fixed Receive Rate 1.45%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext4960MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Short [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 61-72 Months [Member]      
Derivative [Line Items]      
Derivatives, notional amount 25,000invest_DerivativeNotionalAmount
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext6172MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Weighted-average Fixed Pay Rate 1.61%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext6172MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Weighted-average Fixed Receive Rate 1.61%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext6172MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Short [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 73-84 Months [Member]      
Derivative [Line Items]      
Derivatives, notional amount 25,000invest_DerivativeNotionalAmount
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext7384MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Weighted-average Fixed Pay Rate 2.19%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext7384MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Weighted-average Fixed Receive Rate 2.19%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext7384MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Short [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 97-108 Months [Member]      
Derivative [Line Items]      
Derivatives, notional amount 30,000invest_DerivativeNotionalAmount
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext97108MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Weighted-average Fixed Pay Rate 1.93%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext97108MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Weighted-average Fixed Receive Rate 1.93%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext97108MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Short [Member] | Interest Rate Swap [Member] | Interest Rate Swap Agreements, Maturities in Next 109-120 Months [Member]      
Derivative [Line Items]      
Derivatives, notional amount $ 150,000invest_DerivativeNotionalAmount
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext109120MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Weighted-average Fixed Pay Rate 2.17%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext109120MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
Weighted-average Fixed Receive Rate 2.17%us-gaap_DerivativeAverageFixedInterestRate
/ dx_DerivativeInstrumentMaturityScheduleAxis
= dx_InterestRateSwapAgreementsMaturitiesinNext109120MonthsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_PositionAxis
= us-gaap_ShortMember		    
[1] The Eurodollar futures aggregate notional amount represents the total notional of the 3-month contracts with expiration dates from 2015 to 2020. The maximum notional outstanding for any future 3-month period did not exceed $1,300,000 as of December 31, 2014 and $1,175,000 as of December 31, 2013.