Regulatory Capital - Well Capitalized Regulatory Requirements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Actual Amount
Tier 1 Capital (to Average Assets)	$ 3,579,005	$ 3,264,309
Tier 1 Capital (to Risk-Weighted Assets)	3,579,005	3,264,309
Total Capital (to Risk-Weighted Assets)	3,849,820	3,600,668
Tier 1 Capital (to Average Assets)	$ 3,579,005	$ 3,264,309
Actual Ratio
Tier 1 Capital (to Average Assets)	14.00%	12.20%
Tier 1 Capital (to Risk-Weighted Assets)	0.140	0.122
Total Capital (to Risk-Weighted Assets)	0.150	0.134
Tier 1 Capital (to Average Assets)	0.113	0.102
Well Capitalized Regulatory Requirements, Amount
Tier 1 Capital (to Average Assets)	$ 1,794,780	$ 1,876,050
Tier 1 Capital (to Risk-Weighted Assets)	2,179,375	2,278,060
Total Capital (to Risk-Weighted Assets)	2,692,169	2,814,074
Tier 1 Capital (to Average Assets)	$ 1,264,424	$ 1,282,642
Well Capitalized Regulatory Requirements, Ratio
Tier 1 Capital (to Average Assets)	7.00%	7.00%
Tier 1 Capital (to Risk-Weighted Assets)	0.085	0.085
Total Capital (to Risk-Weighted Assets)	0.105	0.105
Tier 1 Capital (to Average Assets)	0.040	0.040

Common Equity Tier One Risk Based Capital

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Tier One Risk Based Capital for Common Equity Required to be Capitalized

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Amount of total capital as defined by regulatory framework.

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Amount of minimum total risk-based capital categorized as well capitalized as defined by regulatory framework for prompt corrective action.

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