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Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Dec. 31, 2017 | Jun. 30, 2017
Allowance for loan losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance | $ 223,967 | $ 248,710 | $ 230,682 | $ 246,159 |  |  |
Provision for loan losses | 1,702 | 3,009 | (3,699) | 4,813 |  |  |
Loans charged off | (15,105) | (2,872) | (17,995) | (5,025) |  |  |
Recoveries | 4,578 | 1,214 | 6,154 | 4,114 |  |  |
Ending balance | 215,142 | 250,061 | 215,142 | 250,061 |  |  |
Allowance for off-balance sheet credit losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance | 4,135 | 9,440 | 3,734 | 11,244 |  |  |
Provision for off-balance sheet credit losses | (1,702) | (3,009) | (1,301) | (4,813) |  |  |
Ending balance | 2,433 | 6,431 | 2,433 | 6,431 |  |  |
Total provision for credit losses | 0 | 0 | (5,000) | 0 |  |  |
Recorded investment [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, recorded investment |  |  |  |  | $ 17,838,039 | $ 16,965,550 | $ 16,938,206
Individually measured for impairment, recorded investment |  |  |  |  | 165,657 | 187,874 | 245,439
Total |  |  |  |  | 18,003,696 | 17,153,424 | 17,183,645
Related allowance [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, related allowance |  |  |  |  | 184,470 | 199,634 | 212,994
Individually measured for impairment, related allowance |  |  |  |  | 15,200 | 8,831 | 9,693
Total | 223,967 | 248,710 | 230,682 | 246,159 | 215,142 | 230,682 | 250,061
Commercial |  |  |  |  |  |  |
Allowance for loan losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance | 120,083 | 137,616 | 124,269 | 140,213 |  |  |
Provision for loan losses | 7,116 | 1,546 | 4,005 | (1,809) |  |  |
Loans charged off | (13,775) | (1,703) | (15,338) | (2,127) |  |  |
Recoveries | 298 | 283 | 786 | 1,465 |  |  |
Ending balance | 113,722 | 137,742 | 113,722 | 137,742 |  |  |
Allowance for off-balance sheet credit losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance | 4,027 | 9,288 | 3,644 | 11,063 |  |  |
Provision for off-balance sheet credit losses | (1,666) | (2,987) | (1,283) | (4,762) |  |  |
Ending balance | 2,361 | 6,301 | 2,361 | 6,301 |  |  |
Total provision for credit losses | 5,450 | (1,441) | 2,722 | (6,571) |  |  |
Recorded investment [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, recorded investment |  |  |  |  | 11,228,061 | 10,596,672 | 10,440,798
Individually measured for impairment, recorded investment |  |  |  |  | 120,978 | 137,303 | 197,157
Total |  |  |  |  | 11,349,039 | 10,733,975 | 10,637,955
Related allowance [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, related allowance |  |  |  |  | 98,522 | 115,438 | 128,049
Individually measured for impairment, related allowance |  |  |  |  | 15,200 | 8,831 | 9,693
Total | 120,083 | 137,616 | 124,269 | 140,213 | 113,722 | 124,269 | 137,742
Commercial real estate |  |  |  |  |  |  |
Allowance for loan losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance | 57,070 | 58,343 | 56,621 | 50,749 |  |  |
Provision for loan losses | (1,409) | 105 | (1,143) | 6,964 |  |  |
Loans charged off | 0 | (76) | 0 | (76) |  |  |
Recoveries | 3,097 | 208 | 3,280 | 943 |  |  |
Ending balance | 58,758 | 58,580 | 58,758 | 58,580 |  |  |
Allowance for off-balance sheet credit losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance | 44 | 106 | 45 | 123 |  |  |
Provision for off-balance sheet credit losses | (27) | (22) | (28) | (39) |  |  |
Ending balance | 17 | 84 | 17 | 84 |  |  |
Total provision for credit losses | (1,436) | 83 | (1,171) | 6,925 |  |  |
Recorded investment [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, recorded investment |  |  |  |  | 3,710,224 | 3,477,132 | 3,684,817
Individually measured for impairment, recorded investment |  |  |  |  | 1,996 | 2,855 | 3,775
Total |  |  |  |  | 3,712,220 | 3,479,987 | 3,688,592
Related allowance [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, related allowance |  |  |  |  | 58,758 | 56,621 | 58,580
Individually measured for impairment, related allowance |  |  |  |  | 0 | 0 | 0
Total | 57,070 | 58,343 | 56,621 | 50,749 | 58,758 | 56,621 | 58,580
Residential mortgage |  |  |  |  |  |  |
Allowance for loan losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance | 18,431 | 18,177 | 18,451 | 18,224 |  |  |
Provision for loan losses | (257) | (47) | (419) | (86) |  |  |
Loans charged off | (135) | (40) | (235) | (276) |  |  |
Recoveries | 505 | 169 | 747 | 397 |  |  |
Ending balance | 18,544 | 18,259 | 18,544 | 18,259 |  |  |
Allowance for off-balance sheet credit losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance | 62 | 40 | 43 | 50 |  |  |
Provision for off-balance sheet credit losses | (9) | (2) | 10 | (12) |  |  |
Ending balance | 53 | 38 | 53 | 38 |  |  |
Total provision for credit losses | (266) | (49) | (409) | (98) |  |  |
Recorded investment [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, recorded investment |  |  |  |  | 1,899,907 | 1,926,239 | 1,894,963
Individually measured for impairment, recorded investment |  |  |  |  | 42,343 | 47,447 | 44,235
Total |  |  |  |  | 1,942,250 | 1,973,686 | 1,939,198
Related allowance [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, related allowance |  |  |  |  | 18,544 | 18,451 | 18,259
Individually measured for impairment, related allowance |  |  |  |  | 0 | 0 | 0
Total | 18,431 | 18,177 | 18,451 | 18,224 | 18,544 | 18,451 | 18,259
Personal |  |  |  |  |  |  |
Allowance for loan losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance | 8,408 | 7,247 | 9,124 | 8,773 |  |  |
Provision for loan losses | 755 | 1,358 | 603 | 570 |  |  |
Loans charged off | (1,195) | (1,053) | (2,422) | (2,546) |  |  |
Recoveries | 678 | 554 | 1,341 | 1,309 |  |  |
Ending balance | 8,646 | 8,106 | 8,646 | 8,106 |  |  |
Allowance for off-balance sheet credit losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance | 2 | 6 | 2 | 8 |  |  |
Provision for off-balance sheet credit losses | 0 | 2 | 0 | 0 |  |  |
Ending balance | 2 | 8 | 2 | 8 |  |  |
Total provision for credit losses | 755 | 1,360 | 603 | 570 |  |  |
Recorded investment [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, recorded investment |  |  |  |  | 999,847 | 965,507 | 917,628
Individually measured for impairment, recorded investment |  |  |  |  | 340 | 269 | 272
Total |  |  |  |  | 1,000,187 | 965,776 | 917,900
Related allowance [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, related allowance |  |  |  |  | 8,646 | 9,124 | 8,106
Individually measured for impairment, related allowance |  |  |  |  | 0 | 0 | 0
Total | 8,408 | 7,247 | 9,124 | 8,773 | 8,646 | 9,124 | 8,106
Specific Allowance [Member] |  |  |  |  |  |  |
Allowance for loan losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance |  |  | 208,465 |  |  |  |
Ending balance | 199,670 | 222,687 | 199,670 | 222,687 |  |  |
Recorded investment [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, recorded investment |  |  |  |  | 17,838,039 | 16,965,550 | 16,938,206
Individually measured for impairment, recorded investment |  |  |  |  | 165,657 | 187,874 | 245,439
Total |  |  |  |  | 18,003,696 | 17,153,424 | 17,183,645
Related allowance [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, related allowance |  |  |  |  | 184,470 | 199,634 | 212,994
Individually measured for impairment, related allowance |  |  |  |  | 15,200 | 8,831 | 9,693
Total | 199,670 | 222,687 | 208,465 | 222,687 | 199,670 | 208,465 | 222,687
Nonspecific Allowance [Member] |  |  |  |  |  |  |
Allowance for loan losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance | 19,975 | 27,327 | 22,217 | 28,200 |  |  |
Provision for loan losses | (4,503) | 47 | (6,745) | (826) |  |  |
Loans charged off | 0 | 0 | 0 | 0 |  |  |
Recoveries | 0 | 0 | 0 | 0 |  |  |
Ending balance | 15,472 | 27,374 | 15,472 | 27,374 |  |  |
Allowance for off-balance sheet credit losses [Roll Forward] |  |  |  |  |  |  |
Beginning balance | 0 | 0 | 0 | 0 |  |  |
Provision for off-balance sheet credit losses | 0 | 0 | 0 | 0 |  |  |
Ending balance | 0 | 0 | 0 | 0 |  |  |
Total provision for credit losses | (4,503) | 47 | (6,745) | (826) |  |  |
Recorded investment [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, recorded investment |  |  |  |  | 0 | 0 | 0
Individually measured for impairment, recorded investment |  |  |  |  | 0 | 0 | 0
Total |  |  |  |  | 0 | 0 | 0
Related allowance [Abstract] |  |  |  |  |  |  |
Collectively measured for impairment, related allowance |  |  |  |  | 0 | 0 | 0
Individually measured for impairment, related allowance |  |  |  |  | 0 | 0 | 0
Total | $ 19,975 | $ 27,327 | $ 22,217 | $ 28,200 | $ 15,472 | $ 22,217 | $ 27,374

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