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Shareholders' Equity, Dividends Restrictions and Other Regulatory Matters (Details) $ in Thousands | 2 Months Ended | 10 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Feb. 20, 2019 shares | Dec. 31, 2018 USD ($) Rate shares | Oct. 31, 2018 shares | Dec. 31, 2018 USD ($) vote Rate shares | Dec. 31, 2017 USD ($) Rate shares | Dec. 31, 2016 USD ($) | Nov. 01, 2018 shares
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |
Capital required for common equity Tier 1 capital to risk-weighted assets |  | 4.50% |  | 4.50% |  |  |
Dividends from subsidiaries |  |  |  | $ 242,910 |  |  |
Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets |  | 6.00% |  | 6.00% |  |  |
Capital Required for Capital Adequacy to Risk Weighted Assets |  | 8.00% |  | 8.00% |  |  |
Leverage Capital Required Ratio To Tangible Assets |  | 4.00% |  | 4.00% |  |  |
Tier 2 capital |  | $ 20,000 |  | $ 20,000 | $ 0 |  |
Subordinated Debt, Annual Tier 2 Discount Percentage | Rate |  | 0.00% |  | 0.00% | 20.00% |  |
Maximum Undivided Profits Elgible For Dividend Payment Without Changing Well Capitalized Status |  | $ 1,092,100 |  | $ 1,092,100 |  |  |
Average Required Maintence Of Non Interst Bearing Reserve Balance |  |  |  | $ 680,300 |  |  |
Capital Conservation Buffer, Annual Percentage Increase |  | 0.625% |  | 0.625% |  |  |
Capital Conservation Buffer |  | 1.88% |  | 1.88% | 0.625% |  |
Fully Phased In 2019 Capital Conservation Buffer |  | 2.50% |  | 2.50% |  |  |
Common Class A [Member] |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |
Votes per share of common stock | vote |  |  |  | 1 |  |  |
Stock Repurchase Program, Number of Shares Authorized to be Repurchased | shares |  | 800,000 |  | 800,000 |  |  | 800,000
Stock Repurchased During Period, Shares | shares |  |  |  | 382,000 | 0 |  |
Stock Repurchased and Retired During Period, Shares | shares |  | 182,000 | 200,000 |  |  |  |
Common Class A [Member] | Subsequent Event |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |
Stock Repurchased and Retired During Period, Shares | shares | 106,500 |  |  |  |  |  |
Class B Common Stock |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |
Votes per share of common stock | vote |  |  |  | 16 |  |  |
Stock Repurchased and Retired During Period, Shares | shares |  |  |  | 0 | 0 |  |
Parent |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |
Dividends from subsidiaries |  |  |  |  | $ 50,424 | $ 90,100 |
BancShares [Member] |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |
Tier 1 Capital for Capital Adequacy |  | $ 3,463,307 |  | $ 3,463,307 | 3,287,364 |  |
Capital Required for Capital Adequacy |  | 3,826,626 |  | 3,826,626 | 3,626,789 |  |
Leverage Capital Required for Capital Adequacy |  | $ 3,463,307 |  | $ 3,463,307 | $ 3,287,364 |  |
Tier 1 Risk Based Capital to Risk Weighted Assets |  | 12.67% |  | 12.67% | 12.88% |  |
Capital to Risk Weighted Assets |  | 13.99% |  | 13.99% | 14.21% |  |
Leverage Capital to Average Assets |  | 9.77% |  | 9.77% | 9.47% |  |
Tier 1 Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets |  | 8.00% |  | 8.00% | 8.00% |  |
Common equity Tier 1 |  | $ 3,463,307 |  | $ 3,463,307 | $ 3,287,364 |  |
Common equity Tier 1 to risk-weighted assets |  | 12.67% |  | 12.67% | 12.88% |  |
Common equity Tier 1 required to be well capitalized to risk-weighted assets |  | 6.50% |  | 6.50% | 6.50% |  |
Capital Required to be Well Capitalized |  | 10.00% |  | 10.00% | 10.00% |  |
Leverage Capital Required to be Well Capitalized to Average Assets |  | 5.00% |  | 5.00% | 5.00% |  |
Capital Conservation Buffer |  | 5.99% |  | 5.99% |  |  |
FCB [Member] |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |
Tier 1 Capital for Capital Adequacy |  | $ 3,315,742 |  | $ 3,315,742 | $ 3,189,709 |  |
Capital Required for Capital Adequacy |  | 3,574,561 |  | 3,574,561 | 3,422,634 |  |
Leverage Capital Required for Capital Adequacy |  | $ 3,315,742 |  | $ 3,315,742 | $ 3,189,709 |  |
Tier 1 Risk Based Capital to Risk Weighted Assets |  | 12.17% |  | 12.17% | 12.54% |  |
Capital to Risk Weighted Assets |  | 13.12% |  | 13.12% | 13.46% |  |
Leverage Capital to Average Assets |  | 9.39% |  | 9.39% | 9.22% |  |
Tier 1 Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets |  | 8.00% |  | 8.00% | 8.00% |  |
Common equity Tier 1 |  | $ 3,315,742 |  | $ 3,315,742 | $ 3,189,709 |  |
Common equity Tier 1 to risk-weighted assets |  | 12.17% |  | 12.17% | 12.54% |  |
Common equity Tier 1 required to be well capitalized to risk-weighted assets |  | 6.50% |  | 6.50% | 6.50% |  |
Capital Required to be Well Capitalized |  | 10.00% |  | 10.00% | 10.00% |  |
Leverage Capital Required to be Well Capitalized to Average Assets |  | 5.00% |  | 5.00% | 5.00% |  |
Capital Conservation Buffer |  | 5.12% |  | 5.12% |  |  |

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