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Shareholders' Equity, Dividends Restrictions and Other Regulatory Matters (Details) $ / shares in Units, $ in Thousands |  | 12 Months Ended
--- | --- | ---
Mar. 12, 2020 shares | Dec. 31, 2020 USD ($) vote $ / shares shares | Dec. 31, 2019 USD ($) $ / shares shares | Dec. 31, 2018 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Capital required for common equity Tier 1 capital to risk-weighted assets |  | 4.50% |  |
Dividends from subsidiaries |  | $ 229,685 |  |
Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets |  | 0.0600 |  |
Capital Required for Capital Adequacy to Risk Weighted Assets |  | 0.0800 |  |
Leverage Capital Required Ratio To Tangible Assets |  | 0.0400 |  |
Stock repurchases during period |  | $ 333,800 | $ 450,800 |
Price of repurchased shares (usd per share) | $ / shares |  | $ 410.48 | $ 451.33 |
Outstanding Shares Repurchased, Percent |  |  | 8.40% | 9.40%
Maximum Undivided Profits Elgible For Dividend Payment Without Changing Well Capitalized Status |  | $ 1,700,000 |  |
Average Required Maintence Of Non Interst Bearing Reserve Balance |  | $ 115,200 |  |
Capital Conservation Buffer |  | 2.50% |  |
Net proceeds from preferred stock issuance |  | $ 339,937 | $ 0 | $ 0
Non-Cumulative Perpetual Preferred Stock, Series A [Member] |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Preferred Stock, dividend rate, percentage |  | 5.375% |  |
Preferred stock, par value (in dollars per share) | $ / shares |  | $ 0.01 |  |
Preferred Stock, Liquidation Preference Per Share | $ / shares |  | 1,000 |  |
Fixed-to-Floating Rate Subordinated Notes Due 2030 [Member] |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Preferred Stock, Liquidation Preference Per Share | $ / shares |  | $ 25 |  |
Qualifying Subordinated Debentures [Member] |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Tier 2 capital |  | $ 377,500 | 32,500 |
Common Class A [Member] |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Votes per share of common stock | vote |  | 1 |  |
Stock repurchases during period |  | $ 333,755 | $ 450,880 | 165,338
Stock Repurchased and Retired During Period, Shares | shares |  | 813,090 | 998,910 |
Class B Common Stock |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Votes per share of common stock | vote |  | 16 |  |
Depositary Shares [Member] |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Stock Issued During Period, Shares, New Issues | shares | 13,800,000 |  |  |
Net proceeds from preferred stock issuance |  | $ 345,000 |  |
Trusted Preferred Capital Securities [Member] |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Tier 2 capital |  | 128,500 | $ 128,500 |
Parent |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Dividends from subsidiaries |  |  | 149,819 | 242,900
Net proceeds from preferred stock issuance |  | 339,937 | 0 | $ 0
BancShares |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Tier 1 Capital for Capital Adequacy |  | 4,577,212 | 3,731,501 |
Capital Required for Capital Adequacy |  | 3,516,149 | 3,344,305 |
Leverage Capital Required for Capital Adequacy |  | $ 3,856,086 | $ 3,344,305 |
Tier 1 Risk Based Capital to Risk Weighted Assets |  | 0.1381 | 0.1212 |
Capital to Risk Weighted Assets |  | 0.1061 | 0.1086 |
Leverage Capital to Average Assets |  | 0.0786 | 0.0881 |
Tier 1 Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets |  | 0.1000 |  |
Common equity Tier 1 |  | $ 3,856,086 | $ 3,344,305 |
Common equity Tier 1 to risk-weighted assets |  | 0.1163 | 0.1086 |
Common equity Tier 1 required to be well capitalized to risk-weighted assets |  | 8.00% |  |
Capital Required to be Well Capitalized |  | 0.0650 |  |
Leverage Capital Required to be Well Capitalized to Average Assets |  | 0.0500 |  |
Capital Conservation Buffer |  |  | 5.63% |
FCB [Member] |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |
Tier 1 Capital for Capital Adequacy |  | $ 4,543,496 | $ 3,837,670 |
Capital Required for Capital Adequacy |  | 4,276,870 | 3,554,974 |
Leverage Capital Required for Capital Adequacy |  | $ 4,276,870 | $ 3,554,974 |
Tier 1 Risk Based Capital to Risk Weighted Assets |  | 0.1372 | 0.1246 |
Capital to Risk Weighted Assets |  | 0.1292 | 0.1154 |
Leverage Capital to Average Assets |  | 0.0872 | 0.0938 |
Tier 1 Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets |  | 0.1000 |  |
Common equity Tier 1 |  | $ 4,276,870 | $ 3,554,974 |
Common equity Tier 1 to risk-weighted assets |  | 0.1292 | 0.1154 |
Common equity Tier 1 required to be well capitalized to risk-weighted assets |  | 8.00% |  |
Capital Required to be Well Capitalized |  | 0.0650 |  |
Leverage Capital Required to be Well Capitalized to Average Assets |  | 0.0500 |  |
Capital Conservation Buffer |  |  | 5.72% |

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- Definition Amount of Tier 2 risk-based capital as defined by regulatory framework. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826 + Details
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