Derivatives and Hedging Activity - Designated and Non-Designated Hedges (Details) - 6 months ended Jun. 30, 2017 € in Thousands, £ in Thousands, SEK in Thousands, NOK in Thousands, DKK in Thousands, $ in Thousands	SEK instrument item	NOK instrument item	GBP (£) instrument item	DKK instrument item	USD ($) instrument item	EUR (€) instrument item
Derivatives
Number of contracts	270	270	270	270	270	270
Foreign exchange contracts | DKK | Buy
Derivatives
Number of contracts	1	1	1	1	1	1
Aggregate notional amount | DKK				DKK 5,947
Foreign exchange contracts | DKK | Sell
Derivatives
Number of contracts	1	1	1	1	1	1
Aggregate notional amount | DKK				DKK 5,960
Foreign exchange contracts | EUR | Buy
Derivatives
Number of contracts	2	2	2	2	2	2
Aggregate notional amount | €						€ 1,728
Foreign exchange contracts | EUR | Sell
Derivatives
Number of contracts	49	49	49	49	49	49
Aggregate notional amount | €						€ 289,453
Foreign exchange contracts | EUR | Sell | Ireland Portfolio
Derivatives
Number of contracts	36	36	36	36	36	36
Aggregate notional amount | €						€ 233,600
Foreign exchange contracts | GBP | Sell
Derivatives
Number of contracts	133	133	133	133	133	133
Aggregate notional amount | £			£ 236,257
Foreign exchange contracts | NOK | Buy
Derivatives
Number of contracts	1	1	1	1	1	1
Aggregate notional amount | $					$ 836
Foreign exchange contracts | NOK | Sell
Derivatives
Number of contracts	1	1	1	1	1	1
Aggregate notional amount | NOK		NOK 836
Foreign exchange contracts | SEK | Buy
Derivatives
Number of contracts	1	1	1	1	1	1
Aggregate notional amount | $					$ 1,138
Foreign exchange contracts | SEK | Sell
Derivatives
Number of contracts	1	1	1	1	1	1
Aggregate notional amount | SEK	SEK 1,317
Interest rate swaps | Derivatives designated as hedging instruments
Derivatives
Number of contracts | instrument	6	6	6	6	6	6
Aggregate notional amount | $					$ 50,500
Hedging period for covering exposure to the variability in future cash flows	47 months
Interest rate swaps | Derivatives designated as hedging instruments | Minimum
Derivatives
Fixed monthly coupons at fixed rate (as a percent)	0.60%	0.60%	0.60%	0.60%	0.60%	0.60%
Interest rate swaps | Derivatives designated as hedging instruments | Maximum
Derivatives
Fixed monthly coupons at fixed rate (as a percent)	1.52%	1.52%	1.52%	1.52%	1.52%	1.52%
Interest rate swaps - Paying fixed rates | USD
Derivatives
Number of contracts	58	58	58	58	58	58
Aggregate notional amount | $					$ 898,640
Interest rate swaps - Receiving fixed rates | USD
Derivatives
Number of contracts	2	2	2	2	2	2
Aggregate notional amount | $					$ 9,600
Interest rate caps | EUR
Derivatives
Number of contracts	2	2	2	2	2	2
Aggregate notional amount | €						€ 294,000
Interest rate caps | USD
Derivatives
Number of contracts	7	7	7	7	7	7
Aggregate notional amount | $					$ 60,066
Interest Rate Swaption | USD
Derivatives
Number of contracts	1	1	1	1	1	1
Aggregate notional amount | $					$ 232,500
Credit index instruments | USD
Derivatives
Number of contracts	10	10	10	10	10	10
Aggregate notional amount | $					$ 59,000