Financial Derivatives - Schedule of Derivative Instruments in Statement of Financial Position (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Notional Disclosures [Abstract]
Notional Amount	$ 15,711,679	$ 15,447,553
Asset
Asset	18,370	17,468
Collateral (held)/pledged	(4,917)	(1,345)
Net amount	13,453	16,123
(Liability)
(Liability)	(28,345)	(29,892)
Collateral (held)/pledged	198,159
Financial derivatives	169,814	182,371
Designated as hedge | Fair value hedges: | Pay fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	5,457,191	5,463,303
Asset
Asset	7,832	10,157
(Liability)
(Liability)	$ (1,517)	$ (2,585)
Weighted- Average Pay Rate	2.25%	2.26%
Weighted- Average Receive Rate	0.19%	0.21%
Weighted- Average Remaining Term (in years)	11 years 11 months 26 days	11 years 11 months 12 days
Designated as hedge | Fair value hedges: | Receive fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 3,587,529	$ 2,611,029
Asset
Asset	76	2
(Liability)
(Liability)	$ (11,143)	$ (8,755)
Weighted- Average Pay Rate	0.25%	0.32%
Weighted- Average Receive Rate	1.21%	1.61%
Weighted- Average Remaining Term (in years)	2 years 3 months 3 days	2 years 1 month 6 days
Designated as hedge | Fair value hedges: | Receive fixed callable
Notional Disclosures [Abstract]
Notional Amount	$ 601,577	$ 343,500
Asset
Asset	2,055	3,108
(Liability)
(Liability)	$ (4,712)	$ (4)
Weighted- Average Pay Rate	0.07%	0.16%
Weighted- Average Receive Rate	0.86%	1.78%
Weighted- Average Remaining Term (in years)	4 years 4 months 6 days	3 years 1 month 28 days
Designated as hedge | Cash flow hedges: | Pay fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 472,000	$ 472,000
Asset
Asset	7,483	2,584
(Liability)
(Liability)	$ (4,022)	$ (8,771)
Weighted- Average Pay Rate	2.04%	2.04%
Weighted- Average Receive Rate	0.54%	0.57%
Weighted- Average Remaining Term (in years)	5 years 9 months 18 days	6 years 14 days
No hedge designation
Asset
Credit valuation adjustment	$ (74)	$ (1)
(Liability)
Credit valuation adjustment	21	35
No hedge designation | Pay fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	338,951	339,090
Asset
Asset	0	0
(Liability)
(Liability)	$ (6,829)	$ (9,675)
Weighted- Average Pay Rate	2.38%	2.38%
Weighted- Average Receive Rate	0.18%	0.19%
Weighted- Average Remaining Term (in years)	3 years 11 months 23 days	4 years 2 months 23 days
No hedge designation | Receive fixed non-callable
Notional Disclosures [Abstract]
Notional Amount	$ 2,258,220	$ 2,359,220
Asset
Asset	0	0
(Liability)
(Liability)	$ 0	$ 0
Weighted- Average Pay Rate	0.14%	0.16%
Weighted- Average Receive Rate	0.70%	0.87%
Weighted- Average Remaining Term (in years)	10 months 24 days	1 year 25 days
No hedge designation | Receive fixed callable
Notional Disclosures [Abstract]
Notional Amount	$ 100,000	$ 200,000
Asset
Asset	0	1
(Liability)
(Liability)	$ 0	$ (12)
Weighted- Average Pay Rate	0.15%	0.13%
Weighted- Average Receive Rate	0.15%	0.15%
Weighted- Average Remaining Term (in years)	6 months	8 months 19 days
No hedge designation | Basis swaps
Notional Disclosures [Abstract]
Notional Amount	$ 2,883,911	$ 3,628,911
Asset
Asset	978	1,617
(Liability)
(Liability)	$ (143)	$ (43)
Weighted- Average Pay Rate	0.15%	0.18%
Weighted- Average Receive Rate	0.19%	0.23%
Weighted- Average Remaining Term (in years)	2 years 3 months 29 days	2 years 10 days
No hedge designation | Treasury futures
Notional Disclosures [Abstract]
Notional Amount	$ 12,300	$ 30,500
Asset
Asset	20	0
(Liability)
(Liability)	$ 0	$ (82)
Weighted- Average Forward Price (in dollars per share)	$ 131.10	$ 137.81