Derivative Financial Instruments (Details) - USD ($) $ in Thousands		6 Months Ended		12 Months Ended
		Jun. 30, 2015		Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Aggregate fair value of derivative instruments with credit-risk-related contingent features, in case of net liability position		$ 139,370		$ 141,653
Collateral related to the derivatives		102,444		106,110
Fair value of assets required to settle the derivatives in, net liability position		36,925
Amount of unrestricted cash collateral to counterparties in the normal course of business		120,107		106,110
Cash collateral received		820		791
Net derivative gains estimated to be reclassified from accumulated other comprehensive income (loss) into net income within the next twelve months		9,035
Derivative financial instruments
Notional amount		8,640,924		1,544,907
Net derivatives, Fair value		(117,815)		(100,983)
Asset derivatives, Fair value		44,646	[1]	35,604	[2]
Liability derivatives, Fair value		162,461	[1]	136,587	[2]
Interest rate swaps
Derivative financial instruments
Average notional amount of the derivative instruments		431,286		340,262
Other forward contracts
Derivative financial instruments
Average notional amount of the derivative instruments		5,807,767		4,217,408
Cross-currency swaps
Derivative financial instruments
Average notional amount of the derivative instruments		875,406		732,581
Future
Derivative financial instruments
Average notional amount of the derivative instruments		21,453		21,702
Swaption
Derivative financial instruments
Average notional amount of the derivative instruments		255,167		407,552
Derivatives designated as hedges:
Derivative financial instruments
Notional amount		487,364		436,445
Net derivatives, Fair value		17,993		21,574
Asset derivatives, Fair value		25,570	[1]	24,526	[2]
Liability derivatives, Fair value		7,577	[1]	2,952	[2]
Derivatives designated as hedges: | Cash flow hedges:
Derivative financial instruments
Notional amount		453,614		358,445
Net derivatives, Fair value		17,355		20,068
Asset derivatives, Fair value		24,923	[1]	22,889	[2]
Liability derivatives, Fair value		7,568	[1]	2,821	[2]
Derivatives designated as hedges: | Cash flow hedges: | Interest rate swaps
Derivative financial instruments
Notional amount		184,200		184,200
Net derivatives, Fair value		15,811		17,746
Asset derivatives, Fair value		15,811	[1]	17,746	[2]
Liability derivatives, Fair value		0	[1]	0	[2]
Derivatives designated as hedges: | Cash flow hedges: | Cross-currency swaps
Derivative financial instruments
Notional amount		269,414		174,245
Net derivatives, Fair value		1,544		2,322
Asset derivatives, Fair value		9,112	[1]	5,143	[2]
Liability derivatives, Fair value		7,568	[1]	2,821	[2]
Derivatives designated as hedges: | Fair value hedges:
Derivative financial instruments
Notional amount		33,750		78,000
Net derivatives, Fair value		638		1,506
Asset derivatives, Fair value		647	[1]	1,637	[2]
Liability derivatives, Fair value		9	[1]	131	[2]
Derivatives designated as hedges: | Fair value hedges: | Interest rate swaps
Derivative financial instruments
Notional amount		33,750		78,000
Net derivatives, Fair value		638		1,506
Asset derivatives, Fair value		647	[1]	1,637	[2]
Liability derivatives, Fair value		9	[1]	131	[2]
Derivatives not designated as hedges:
Derivative financial instruments
Notional amount		8,153,560		1,108,462
Net derivatives, Fair value		(135,808)		(122,557)
Asset derivatives, Fair value		19,076	[1]	11,078	[2]
Liability derivatives, Fair value		154,884	[1]	133,635	[2]
Derivatives not designated as hedges: | Interest rate swaps
Derivative financial instruments
Notional amount		250,600		128,100
Net derivatives, Fair value		(1,559)		4,402
Asset derivatives, Fair value		4,620	[1]	6,246	[2]
Liability derivatives, Fair value		6,179	[1]	1,844	[2]
Derivatives not designated as hedges: | Futures on equity indices
Derivative financial instruments
Notional amount		18,006		5,505
Net derivatives, Fair value		0		0
Asset derivatives, Fair value		0	[1]	0	[2]
Liability derivatives, Fair value		0	[1]	0	[2]
Derivatives not designated as hedges: | Interest rate futures
Derivative financial instruments
Notional amount		8,795		17,958
Net derivatives, Fair value		0		0
Asset derivatives, Fair value		0	[1]	0	[2]
Liability derivatives, Fair value		0	[1]	0	[2]
Derivatives not designated as hedges: | Interest rate swaptions
Derivative financial instruments
Notional amount		192,724		293,964
Net derivatives, Fair value		260		271
Asset derivatives, Fair value		260	[1]	271	[2]
Liability derivatives, Fair value		0	[1]	0	[2]
Derivatives not designated as hedges: | Other forward contracts
Derivative financial instruments
Notional amount		7,020,500
Net derivatives, Fair value		(17,760)
Asset derivatives, Fair value	[1]	7,157
Liability derivatives, Fair value	[1]	24,917
Derivatives not designated as hedges: | Cross-currency swaps
Derivative financial instruments
Notional amount		662,935		662,935
Net derivatives, Fair value		(116,749)		(127,230)
Asset derivatives, Fair value		7,039	[1]	4,561	[2]
Liability derivatives, Fair value		$ 123,788	[1]	$ 131,791	[2]

[1] The estimated fair value excludes accrued income and expense. The estimated fair value of all derivatives in an asset position is reported within other assets and the estimated fair value of all derivatives in a liability position is reported within other liabilities in the condensed consolidated balance sheets.

[2] The estimated fair value excludes accrued income and expense. The estimated fair value of all derivatives in an asset position is reported within other assets and the estimated fair value of all derivatives in a liability position is reported within other liabilities in the condensed consolidated balance sheets.