Derivative Financial Instruments (Details) - USD ($) $ in Thousands		9 Months Ended		12 Months Ended
		Sep. 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		$ 101,896		$ 141,653
Collateral related to the derivatives		66,769		106,110
Fair value of assets required to settle the derivatives in, net liability position		35,127
Amount of unrestricted cash collateral to counterparties in the normal course of business		66,769		106,110
Cash collateral received		15,168		791
Net derivative gains estimated to be reclassified from accumulated other comprehensive income (loss) into net income within the next twelve months		9,614
Derivative financial instruments
Notional amount		6,901,901		1,544,907
Net derivatives, Fair value		(28,214)		(100,983)
Asset derivatives, Fair value		79,022	[1]	35,604	[2]
Liability derivatives, Fair value		107,236	[1]	136,587	[2]
Interest rate swaps
Derivative financial instruments
Average notional amount of the derivative instruments		439,045		340,262
Other forward contracts
Derivative financial instruments
Average notional amount of the derivative instruments		5,761,678		4,217,408
Cross-currency swaps
Derivative financial instruments
Average notional amount of the derivative instruments		909,195		732,581
Future
Derivative financial instruments
Average notional amount of the derivative instruments		101,382		21,702
Swaption
Derivative financial instruments
Average notional amount of the derivative instruments		230,628		407,552
Derivatives designated as hedges:
Derivative financial instruments
Notional amount		527,384		436,445
Net derivatives, Fair value		30,370		21,574
Asset derivatives, Fair value		31,353	[1]	24,526	[2]
Liability derivatives, Fair value		983	[1]	2,952	[2]
Derivatives designated as hedges: | Cash flow hedges:
Derivative financial instruments
Notional amount		518,634		358,445
Net derivatives, Fair value		30,352		20,068
Asset derivatives, Fair value		31,335	[1]	22,889	[2]
Liability derivatives, Fair value		983	[1]	2,821	[2]
Derivatives designated as hedges: | Cash flow hedges: | Interest rate swaps
Derivative financial instruments
Notional amount		175,800		184,200
Net derivatives, Fair value		13,960		17,746
Asset derivatives, Fair value		13,960	[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		342,834		174,245
Net derivatives, Fair value		16,392		2,322
Asset derivatives, Fair value		17,375	[1]	5,143	[2]
Liability derivatives, Fair value		983	[1]	2,821	[2]
Derivatives designated as hedges: | Fair value hedges:
Derivative financial instruments
Notional amount		8,750		78,000
Net derivatives, Fair value		18		1,506
Asset derivatives, Fair value		18	[1]	1,637	[2]
Liability derivatives, Fair value		0	[1]	131	[2]
Derivatives designated as hedges: | Fair value hedges: | Interest rate swaps
Derivative financial instruments
Notional amount		8,750		78,000
Net derivatives, Fair value		18		1,506
Asset derivatives, Fair value		18	[1]	1,637	[2]
Liability derivatives, Fair value		0	[1]	131	[2]
Derivatives not designated as hedges:
Derivative financial instruments
Notional amount		6,374,517		1,108,462
Net derivatives, Fair value		(58,584)		(122,557)
Asset derivatives, Fair value		47,669	[1]	11,078	[2]
Liability derivatives, Fair value		106,253	[1]	133,635	[2]
Derivatives not designated as hedges: | Interest rate swaps
Derivative financial instruments
Notional amount		276,600		128,100
Net derivatives, Fair value		4,905		4,402
Asset derivatives, Fair value		10,057	[1]	6,246	[2]
Liability derivatives, Fair value		5,152	[1]	1,844	[2]
Derivatives not designated as hedges: | Futures on equity indices
Derivative financial instruments
Notional amount		34,778		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		120,000		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		142,704		293,964
Net derivatives, Fair value		193		271
Asset derivatives, Fair value		193	[1]	271	[2]
Liability derivatives, Fair value		0	[1]	0	[2]
Derivatives not designated as hedges: | Other forward contracts
Derivative financial instruments
Notional amount		5,137,500
Net derivatives, Fair value		14,778
Asset derivatives, Fair value	[1]	23,519
Liability derivatives, Fair value	[1]	8,741
Derivatives not designated as hedges: | Cross-currency swaps
Derivative financial instruments
Notional amount		662,935		662,935
Net derivatives, Fair value		(78,460)		(127,230)
Asset derivatives, Fair value		13,900	[1]	4,561	[2]
Liability derivatives, Fair value		$ 92,360	[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.