Regulatory Capital - Well Capitalized Regulatory Requirements (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Actual Amount
Common Equity Tier I Capital (to Risk-Weighted Assets)	$ 2,494,964	$ 2,350,081
Tier 1 Capital (to Risk-Weighted Assets)	2,494,964	2,350,081
Total Capital (to Risk-Weighted Assets)	2,761,446	2,597,926
Tier 1 Capital (to Average Assets)	$ 2,494,964	$ 2,350,081
Actual Ratio
Common Equity Tier I Capital (to Risk-Weighted Assets)	11.70%	11.90%
Tier 1 Capital (to Risk-Weighted Assets)	11.70%	11.90%
Total Capital (to Risk-Weighted Assets)	13.00%	13.10%
Tier 1 Capital (to Average Assets)	11.00%	11.00%
Well Capitalized Regulatory Requirements, Amount
Common Equity Tier I Capital (to Risk-Weighted Assets)	$ 1,385,322	$ 1,288,435
Tier 1 Capital (to Risk-Weighted Assets)	1,705,011	1,585,767
Total Capital (to Risk-Weighted Assets)	2,131,264	1,982,208
Tier 1 Capital (to Average Assets)	$ 1,138,524	$ 1,067,739
Well Capitalized Regulatory Requirements, Ratio
Common Equity Tier I Capital (to Risk-Weighted Assets)	6.50%	6.50%
Tier 1 Capital (to Risk-Weighted Assets)	8.00%	8.00%
Total Capital (to Risk-Weighted Assets)	10.00%	10.00%
Tier 1 Capital (to Average Assets)	5.00%	5.00%

Common Equity Capital Required to Be Well Capitalized Percent

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Common Equity Tier 1 to Risk Weighted Assets

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common equity capital required to be well capitalized

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common equity tier 1 capital

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The amount of total capital as defined in the regulations.

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The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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Total Capital divided by risk weighted assets as defined in the regulations.

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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

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Tier 1 Leverage Capital divided by average assets as defined in the regulations.

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Tier 1 Risk Based Capital as defined in the regulations.

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The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

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Tier 1 capital divided by risk weighted assets as defined by regulations.

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