Summary of Regulatory Capital Levels [Table Text Block] |
A summary of regulatory capital minimum requirements and levels follows (dollars in thousands): | | | | | | | | | | | | | | | | | Minimum Capital Requirement1 | | Capital Conservation Buffer2 | | Minimum Capital Requirement Including Capital Conservation Buffer | | December 31, 2015 | Total Capital (to Risk Weighted Assets): | | | | | | | | | | | Consolidated | | 4.50% | | 2.50% | | 7.00% | | $ | 3,116,144 |
| | 13.30 | % | BOKF, NA | | 4.50% | | N/A | | 4.50% | | 2,657,935 |
| | 11.43 | % | Common equity Tier 1 Capital (to Risk Weighted Assets): | | | | | | | | | | | Consolidated | | 6.00% | | 2.50% | | 8.50% | | 2,842,193 |
| | 12.13 | % | BOKF, NA | | 6.00% | | N/A | | 6.00% | | 2,385,323 |
| | 10.26 | % | Tier I Capital (to Risk Weighted Assets): | | | | | | | | | | | Consolidated | | 8.00% | | 2.50% | | 10.50% | | $ | 2,842,193 |
| | 12.13 | % | BOKF, NA | | 8.00% | | N/A | | 8.00% | | 2,385,323 |
| | 10.26 | % | Tier I Capital (to Average Assets): | | | | | | | | | | | Consolidated | | 4.00% | | N/A | | 4.00% | | $ | 2,842,193 |
| | 9.25 | % | BOKF, NA | | 4.00% | | N/A | | 4.00% | | 2,385,323 |
| | 7.81 | % |
| | 1 | Effective January 1, 2015 |
| | 2 | Effective January 1, 2016 |
A summary of regulatory capital levels under then current capital rules follows as of December 31, 2014 (dollars in thousands): | | | | | | | | | | | | | | 2014 | Total Capital (to Risk Weighted Assets): | | | | | Consolidated | | $ | 3,120,223 |
| | 14.66 | % | BOKF, NA | | 2,449,078 |
| | 11.56 | % | Tier I Capital (to Risk Weighted Assets): | | | | | Consolidated | | $ | 2,838,129 |
| | 13.33 | % | BOKF, NA | | 2,168,161 |
| | 10.24 | % | Tier I Capital (to Average Assets): | | | | | Consolidated | | $ | 2,838,129 |
| | 9.96 | % | BOKF, NA | | 2,168,161 |
| | 7.65 | % |
|
Accumulated Other Comprehensive Income (Loss) [Table Text Block] |
A rollforward of the components of accumulated other comprehensive income (loss) is included as follows (in thousands): | | | | | | | | | | | | | | | | | | | | | | | | Unrealized Gain (Loss) on | | | | | | | Available for Sale Securities | | Investment Securities Transferred from AFS | | Employee Benefit Plans | | Loss on Effective Cash Flow Hedges | | Total | Balance, December 31, 2012 | | $ | 155,553 |
| | $ | 3,078 |
| | $ | (8,296 | ) | | $ | (415 | ) | | $ | 149,920 |
| Net change in unrealized gain (loss) | | (284,104 | ) | | — |
| | 8,159 |
| | — |
| | (275,945 | ) | Reclassification adjustments included in earnings: | | | | | | | | | | | Interest revenue, Investment securities, Taxable securities | | — |
| | (3,210 | ) | | — |
| | — |
| | (3,210 | ) | Interest expense, Subordinated debentures | | — |
| | — |
| | — |
| | 262 |
| | 262 |
| Net impairment losses recognized in earnings | | 2,308 |
| | — |
| | — |
| | — |
| | 2,308 |
| Gain on available for sale securities, net | | (10,720 | ) | | — |
| | — |
| | — |
| | (10,720 | ) | Other comprehensive income (loss), before income taxes | | (292,516 | ) | | (3,210 | ) | | 8,159 |
| | 262 |
| | (287,305 | ) | Federal and state income tax1 | | (113,788 | ) | | (1,250 | ) | | 3,174 |
| | 102 |
| | (111,762 | ) | Other comprehensive income (loss), net of income taxes | | (178,728 | ) |
| (1,960 | ) |
| 4,985 |
|
| 160 |
|
| (175,543 | ) | Balance, December 31, 2013 | | (23,175 | ) | | 1,118 |
| | (3,311 | ) | | (255 | ) | | (25,623 | ) | Net change in unrealized gain (loss) | | 136,050 |
| | — |
| | 725 |
| | — |
| | 136,775 |
| Reclassification adjustments included in earnings: | | | | | | | | | | | Interest revenue, Investment securities, Taxable securities | | — |
| | (1,216 | ) | | — |
| | — |
| | (1,216 | ) | Interest expense, Subordinated debentures | | — |
| | — |
| | — |
| | 296 |
| | 296 |
| Net impairment losses recognized in earnings | | 373 |
| | — |
| | — |
| | — |
| | 373 |
| Gain on available for sale securities, net | | (1,539 | ) | | — |
| | — |
| | — |
| | (1,539 | ) | Other comprehensive income (loss), before income taxes | | 134,884 |
| | (1,216 | ) | | 725 |
| | 296 |
| | 134,689 |
| Federal and state income tax1 | | 52,470 |
| | (474 | ) | | 282 |
| | 115 |
| | 52,393 |
| Other comprehensive income (loss), net of income taxes | | 82,414 |
|
| (742 | ) |
| 443 |
|
| 181 |
|
| 82,296 |
| Balance, December 31, 2014 | | 59,239 |
| | 376 |
| | (2,868 | ) | | (74 | ) | | 56,673 |
| Net change in unrealized gain (loss) | | (48,607 | ) | | — |
| | 1,804 |
| | — |
| | (46,803 | ) | Reclassification adjustments included in earnings: | | | | | | | | | | | Interest revenue, Investment securities, Taxable securities | | — |
| | (503 | ) | | — |
| | — |
| | (503 | ) | Interest expense, Subordinated debentures | | — |
| | — |
| | — |
| | 121 |
| | 121 |
| Net impairment losses recognized in earnings | | 1,819 |
| | — |
| | — |
| | — |
| | 1,819 |
| Gain on available for sale securities, net | | (12,058 | ) | | — |
| | — |
| | — |
| | (12,058 | ) | Other comprehensive income (loss), before income taxes | | (58,846 | ) | | (503 | ) | | 1,804 |
| | 121 |
| | (57,424 | ) | Federal and state income tax1 | | (22,891 | ) | | (195 | ) | | 701 |
| | 47 |
| | (22,338 | ) | Other comprehensive income (loss), net of income taxes | | (35,955 | ) |
| (308 | ) |
| 1,103 |
|
| 74 |
|
| (35,086 | ) | Balance, December 31, 2015 | | $ | 23,284 |
| | $ | 68 |
| | $ | (1,765 | ) | | $ | — |
| | $ | 21,587 |
|
| | 1 | Calculated using 39% effective tax rate. |
|