Fair Value Measurements - Notional Amounts and Fair Values of Derivatives by Product (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	$ 505,613	$ 297,727
Derivatives asset, Fair Value	2,901	1,663
Derivative Liability, Notional Amount	4,663,277	4,756,631
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	4,130	2,024
Commodity Contracts [Member] \| Future [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	3,702,000	4,059,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	853	166
Other Contracts [Member] \| Foreign Exchange Forward [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	400	200
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	8	1
Other Contracts [Member] \| Forward Start Repurchase Agreement [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	574,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0
To Be Announced Security [Member] \| Other Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	314,255	169,500
Derivatives asset, Fair Value	1,257	332
Derivative Liability, Notional Amount	309,555	169,500
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	1,180	289
TBA Purchase Contracts [Member] \| Other Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	62,358	121,573
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	1,835	923
Tba Sale Agreements [Member] \| Other Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	62,358	121,573
Derivatives asset, Fair Value	1,644	482
Reverse Repurchase Agreement [Member] \| Other Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	129,000
Derivatives asset, Fair Value	0
Auction Rate Securities Purchase Commitment [Member] \| Other Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	14,964	24,358
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ 254	$ 645

Nominal or face amount used to calculate payments on the derivative asset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5580258-113959

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Nominal or face amount used to calculate payments on the derivative liability.

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No definition available.

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