Derivative Financial Instruments (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Derivative financial instruments
Notional amount		$ 2,396,297	$ 1,788,922
Net derivatives, Fair value		108,104	(7,773)
Asset derivatives, Fair value	[1]	146,385	68,600
Liability derivatives, Fair value	[1]	38,281	76,373
Derivatives designated as hedges
Derivative financial instruments
Notional amount		1,034,008	524,673
Net derivatives, Fair value		78,737	40,557
Asset derivatives, Fair value	[1]	87,031	40,579
Liability derivatives, Fair value	[1]	8,294	22
Derivatives designated as hedges | Cash flow hedges
Derivative financial instruments
Notional amount		1,034,008	524,673
Net derivatives, Fair value		78,737	40,557
Asset derivatives, Fair value	[1]	87,031	40,579
Liability derivatives, Fair value	[1]	8,294	22
Derivatives designated as hedges | Cash flow hedges | Interest rate swaps
Derivative financial instruments
Notional amount		419,800	143,800
Net derivatives, Fair value		33,390	11,843
Asset derivatives, Fair value	[1]	33,390	11,843
Derivatives designated as hedges | Cash flow hedges | Cross-currency swaps
Derivative financial instruments
Notional amount		614,208	380,873
Net derivatives, Fair value		45,347	28,714
Asset derivatives, Fair value	[1]	53,641	28,736
Liability derivatives, Fair value	[1]	8,294	22
Derivatives not designated as hedges
Derivative financial instruments
Notional amount		1,362,289	1,264,249
Net derivatives, Fair value		29,367	(48,330)
Asset derivatives, Fair value	[1]	59,354	28,021
Liability derivatives, Fair value	[1]	29,987	76,351
Derivatives not designated as hedges | Interest rate swaps
Derivative financial instruments
Notional amount		468,100	303,600
Net derivatives, Fair value		(4,358)	3,240
Asset derivatives, Fair value	[1]	8,982	8,295
Liability derivatives, Fair value	[1]	13,340	5,055
Derivatives not designated as hedges | Cross-currency swaps
Derivative financial instruments
Notional amount		612,733	662,935
Net derivatives, Fair value		33,371	(51,759)
Asset derivatives, Fair value	[1]	50,018	19,537
Liability derivatives, Fair value	[1]	16,647	71,296
Derivatives not designated as hedges | Futures on equity indices
Derivative financial instruments
Notional amount		34,422	29,310
Derivatives not designated as hedges | Interest rate futures
Derivative financial instruments
Notional amount		81,500	117,200
Derivatives not designated as hedges | Interest rate swaptions
Derivative financial instruments
Notional amount		165,534	151,204
Net derivatives, Fair value		354	189
Asset derivatives, Fair value	[1]	$ 354	$ 189

[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.