Derivative Financial Instruments (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
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	$ 58,305,000	$ 38,324,000
Collateral related to the derivatives	910,000	0
Fair value of assets required to settle the derivatives in, net liability position	57,395,000
Amount of unrestricted cash collateral to counterparties in the normal course of business	910,000	0
Collateral under derivative counterparty collateral agreements	60,919,000	103,214,000
Net derivative gains estimated to be reclassified from accumulated other comprehensive income (loss) into net income within the next twelve months	10,378,000
Derivative financial instruments
Notional amount	5,476,954,000	2,396,297,000
Net derivatives, Fair value	57,212,000	108,104,000
Asset derivatives, Fair value	119,183,000	146,385,000
Liability derivatives, Fair value	61,971,000	38,281,000
Interest rate swaps
Derivative financial instruments
Average notional amount of the derivative instruments	901,471,000	784,900,000
Cross-currency swaps
Derivative financial instruments
Average notional amount of the derivative instruments	1,274,171,000	1,141,967,000
Other forward contracts
Derivative financial instruments
Average notional amount of the derivative instruments	2,102,629,000	2,230,167,000
Future
Derivative financial instruments
Average notional amount of the derivative instruments	114,737,000	145,658,000
Swaption
Derivative financial instruments
Average notional amount of the derivative instruments	162,401,000	156,632,000
Derivatives designated as hedges:
Derivative financial instruments
Notional amount	1,134,134,000	1,034,008,000
Net derivatives, Fair value	50,201,000	78,737,000
Asset derivatives, Fair value	70,253,000	87,031,000
Liability derivatives, Fair value	20,052,000	8,294,000
Derivatives designated as hedges: | Cash flow hedges:
Derivative financial instruments
Notional amount	1,134,134,000	1,034,008,000
Net derivatives, Fair value	50,201,000	78,737,000
Asset derivatives, Fair value	70,253,000	87,031,000
Liability derivatives, Fair value	20,052,000	8,294,000
Derivatives designated as hedges: | Cash flow hedges: | Interest rate swaps
Derivative financial instruments
Notional amount	419,800,000	419,800,000
Net derivatives, Fair value	29,929,000	33,390,000
Asset derivatives, Fair value	29,929,000	33,390,000
Liability derivatives, Fair value	0	0
Derivatives designated as hedges: | Cash flow hedges: | Cross-currency swaps
Derivative financial instruments
Notional amount	714,334,000	614,208,000
Net derivatives, Fair value	20,272,000	45,347,000
Asset derivatives, Fair value	40,324,000	53,641,000
Liability derivatives, Fair value	20,052,000	8,294,000
Derivatives not designated as hedges:
Derivative financial instruments
Notional amount	4,342,820,000	1,362,289,000
Net derivatives, Fair value	7,011,000	29,367,000
Asset derivatives, Fair value	48,930,000	59,354,000
Liability derivatives, Fair value	41,919,000	29,987,000
Derivatives not designated as hedges: | Interest rate swaps
Derivative financial instruments
Notional amount	494,100,000	468,100,000
Net derivatives, Fair value	(2,196,000)	(4,358,000)
Asset derivatives, Fair value	10,296,000	8,982,000
Liability derivatives, Fair value	12,492,000	13,340,000
Derivatives not designated as hedges: | Cross-currency swaps
Derivative financial instruments
Notional amount	612,733,000	612,733,000
Net derivatives, Fair value	11,583,000	33,371,000
Asset derivatives, Fair value	35,587,000	50,018,000
Liability derivatives, Fair value	24,004,000	16,647,000
Derivatives not designated as hedges: | Futures on equity indices
Derivative financial instruments
Notional amount	28,243,000	34,422,000
Net derivatives, Fair value	0	0
Asset derivatives, Fair value	0	0
Liability derivatives, Fair value	0	0
Derivatives not designated as hedges: | Interest rate futures
Derivative financial instruments
Notional amount	88,500,000	81,500,000
Net derivatives, Fair value	0	0
Asset derivatives, Fair value	0	0
Liability derivatives, Fair value	0	0
Derivatives not designated as hedges: | Interest rate swaptions
Derivative financial instruments
Notional amount	161,294,000	165,534,000
Net derivatives, Fair value	204,000	354,000
Asset derivatives, Fair value	204,000	354,000
Liability derivatives, Fair value	0	$ 0
Derivatives not designated as hedges: | Other forward contracts
Derivative financial instruments
Notional amount	2,957,950,000
Net derivatives, Fair value	(2,580,000)
Asset derivatives, Fair value	2,843,000
Liability derivatives, Fair value	$ 5,423,000