Derivatives and Hedging Activity - Designated and Non-Designated Hedges (Details) - 3 months ended Mar. 31, 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	244	244	244	244	244	244
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	54	54	54	54	54	54
Aggregate notional amount | €						€ 293,552
Foreign exchange contracts | EUR | Sell | Ireland Portfolio
Derivatives
Number of contracts	39	39	39	39	39	39
Aggregate notional amount | €						€ 236,700
Foreign exchange contracts | GBP | Sell
Derivatives
Number of contracts	130	130	130	130	130	130
Aggregate notional amount | £			£ 215,690
Foreign exchange contracts | NOK | Buy
Derivatives
Number of contracts	1	1	1	1	1	1
Aggregate notional amount | NOK		NOK 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 | SEK	SEK 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 | Paying fixed rates
Derivatives
Number of contracts	37	37	37	37	37	37
Aggregate notional amount | $					$ 780,033
Interest rate swaps | Receiving fixed rates
Derivatives
Number of contracts	1	1	1	1	1	1
Aggregate notional amount | $					$ 8,000
Interest rate swaps | Derivatives designated as hedging instruments
Derivatives
Number of contracts | instrument	6	6	6	6	6	6
Aggregate notional amount | $					$ 53,000
Fixed monthly coupons at fixed rate, low end of range (as a percent)	0.60%	0.60%	0.60%	0.60%	0.60%	0.60%
Fixed monthly coupons at fixed rate, high end of range (as a percent)	1.52%	1.52%	1.52%	1.52%	1.52%	1.52%
Hedging period for covering exposure to the variability in future cash flows	50 months
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 | $					$ 60,138
Credit index instruments | USD
Derivatives
Number of contracts	5	5	5	5	5	5
Aggregate notional amount | $					$ 34,000