Derivative Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
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	$ 141,653		$ 167,743
Collateral related to the derivatives	106,110		143,540
Fair value of assets required to settle the derivatives in, net liability position	35,543
Amount of unrestricted cash collateral to counterparties in the normal course of business	106,110		143,710
Net derivative gains estimated to be reclassified from accumulated other comprehensive income (loss) into net income within the next twelve months	8,500
Derivative financial instruments
Notional amount	1,544,907		1,492,511
Net derivatives, Fair value	(100,983)	[1]	(144,265)	[1]
Asset derivatives, Fair value	35,604	[1]	23,478	[1]
Liability derivatives, Fair value	136,587	[1]	167,743	[1]
Cross-currency swaps
Derivative financial instruments
Average notional amount of the derivative instruments	340,262		351,579
Other forward contracts
Derivative financial instruments
Average notional amount of the derivative instruments	4,217,408		3,543,173
Cross-currency swaps
Derivative financial instruments
Average notional amount of the derivative instruments	732,581		608,787
Futures
Derivative financial instruments
Average notional amount of the derivative instruments	21,702		46,564
Swaption
Derivative financial instruments
Average notional amount of the derivative instruments	407,552		606,374
Derivatives designated as hedges
Derivative financial instruments
Notional amount	436,445		364,745
Net derivatives, Fair value	21,574	[1]	10,937	[1]
Asset derivatives, Fair value	24,526	[1]	18,927	[1]
Liability derivatives, Fair value	2,952	[1]	7,990	[1]
Derivatives designated as hedges | Cash flow hedges
Derivative financial instruments
Notional amount	358,445		286,745
Net derivatives, Fair value	20,068	[1]	5,986	[1]
Asset derivatives, Fair value	22,889	[1]	13,829	[1]
Liability derivatives, Fair value	2,821	[1]	7,843	[1]
Derivatives designated as hedges | Cash flow hedges | Cross-currency swaps
Derivative financial instruments
Notional amount	184,200		184,200
Net derivatives, Fair value	17,746	[1]	13,829	[1]
Asset derivatives, Fair value	17,746	[1]	13,829	[1]
Derivatives designated as hedges | Cash flow hedges | Cross-currency swaps
Derivative financial instruments
Notional amount	174,245		102,545
Net derivatives, Fair value	2,322	[1]	(7,843)	[1]
Asset derivatives, Fair value	5,143	[1]	0	[1]
Liability derivatives, Fair value	2,821	[1]	7,843	[1]
Derivatives designated as hedges | Fair value hedges
Derivative financial instruments
Notional amount	78,000		78,000
Net derivatives, Fair value	1,506	[1]	4,951	[1]
Asset derivatives, Fair value	1,637	[1]	5,098	[1]
Liability derivatives, Fair value	131	[1]	147	[1]
Derivatives designated as hedges | Fair value hedges | Cross-currency swaps
Derivative financial instruments
Notional amount	78,000		78,000
Net derivatives, Fair value	1,506	[1]	4,951	[1]
Asset derivatives, Fair value	1,637	[1]	5,098	[1]
Liability derivatives, Fair value	131	[1]	147	[1]
Derivatives not designated as hedges
Derivative financial instruments
Notional amount	1,108,462		1,127,766
Net derivatives, Fair value	(122,557)	[1]	(155,202)	[1]
Asset derivatives, Fair value	11,078	[1]	4,551	[1]
Liability derivatives, Fair value	133,635	[1]	159,753	[1]
Derivatives not designated as hedges | Cross-currency swaps
Derivative financial instruments
Notional amount	128,100		55,600
Net derivatives, Fair value	4,402	[1]	(2,038)	[1]
Asset derivatives, Fair value	6,246	[1]	1,454	[1]
Liability derivatives, Fair value	1,844	[1]	3,492	[1]
Derivatives not designated as hedges | Futures on equity indices
Derivative financial instruments
Notional amount	5,505		3,483
Derivatives not designated as hedges | Interest rate futures
Derivative financial instruments
Notional amount	17,958		16,233
Derivatives not designated as hedges | Interest rate swaptions
Derivative financial instruments
Notional amount	293,964		494,774
Net derivatives, Fair value	271	[1]	1,176	[1]
Asset derivatives, Fair value	271	[1]	1,176	[1]
Derivatives not designated as hedges | Cross-currency swaps
Derivative financial instruments
Notional amount	662,935		557,676
Net derivatives, Fair value	(127,230)	[1]	(154,340)	[1]
Asset derivatives, Fair value	4,561	[1]	1,921	[1]
Liability derivatives, Fair value	$ 131,791	[1]	$ 156,261	[1]

[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 consolidated balance sheets.