| Schedule Of Condensed Income Statement And Comprehensive Income Table [Text Block] |
Condensed Income Statements | | | | | | | | | | | | | | | | Year Ended December 31, | | | 2019 | | 2018 | | 2017 | | | (in thousands) | Income: | | | | | | | Dividends from subsidiaries | | $ | 134,000 |
| | $ | 152,116 |
| | $ | 97,264 |
| Interest income | | 2,818 |
| | 2,905 |
| | 2,547 |
| Non-interest income | | 5,112 |
| | 761 |
| | 2,470 |
| Total income | | 141,930 |
| | 155,782 |
| | 102,281 |
| Expense: | | | | | | | Interest expense | | 14,554 |
| | 13,949 |
| | 11,459 |
| Non-interest expense | | 19,543 |
| | 19,025 |
| | 16,293 |
| Total expense | | 34,097 |
| | 32,974 |
| | 27,752 |
| Income before income taxes and equity in undistributed earnings of subsidiaries | | 107,833 |
| | 122,808 |
| | 74,529 |
| Income tax benefit | | 5,628 |
| | 10,436 |
| | 5,229 |
| Income before equity in undistributed earnings of subsidiaries | | 113,461 |
| | 133,244 |
| | 79,758 |
| Equity in undistributed earnings of subsidiaries | | 385,710 |
| | 302,544 |
| | 245,734 |
| Net income | | $ | 499,171 |
| | $ | 435,788 |
| | $ | 325,492 |
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| Condensed Cash Flow Statement [Table Text Block] |
Condensed Statements of Cash Flows | | | | | | | | | | | | | | Year Ended December 31, | | 2019 | | 2018 | | 2017 | | (in thousands) | Cash flows from operating activities: | | | | | | Net income | $ | 499,171 |
| | $ | 435,788 |
| | $ | 325,492 |
| Adjustments to reconcile net income to net cash provided by operating activities: | | | | | | Equity in net undistributed earnings of subsidiaries | (385,710 | ) | | (302,544 | ) | | (245,734 | ) | Other operating activities, net | 9,885 |
| | (5,889 | ) | | 16,921 |
| Net cash provided by operating activities | 123,346 |
| | 127,355 |
| | 96,679 |
| Cash flows from investing activities: | | | | | | Purchases of securities | (10,841 | ) | | (44,409 | ) | | (11,765 | ) | Principal pay downs, calls, maturities, and sales proceeds of securities | 19,032 |
| | 11,362 |
| | 23,196 |
| Capital contributions to subsidiaries | — |
| | — |
| | (50,000 | ) | Other investing activities, net | 7 |
| | (7 | ) | | — |
| Net cash provided by (used in) investing activities | 8,198 |
| | (33,054 | ) | | (38,569 | ) | Cash flows from financing activities: | | | | | | Share repurchases | (120,131 | ) | | (35,688 | ) | | — |
| Other financing activities, net | 80 |
| | 554 |
| | (12,965 | ) | Dividends paid on common stock | (51,329 | ) | | — |
| | — |
| Net cash used in financing activities | (171,380 | ) | | (35,134 | ) | | (12,965 | ) | Net (decrease) increase in cash and cash equivalents | (39,836 | ) | | 59,167 |
| | 45,145 |
| Cash and cash equivalents at beginning of year | 115,721 |
| | 56,554 |
| | 11,409 |
| Cash and cash equivalents at end of year | $ | 75,885 |
| | $ | 115,721 |
| | $ | 56,554 |
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