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Available for Sale Securities (Details) $ in Thousands | 3 Months Ended | 6 Months Ended |
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Jun. 30, 2018 USD ($) | Jun. 30, 2017 USD ($) | Jun. 30, 2018 USD ($) | Jun. 30, 2017 USD ($) | Dec. 31, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  | $ 8,343,468 |  | $ 8,325,000 |  | $ 8,343,468 |  | $ 8,325,000 |  | $ 8,369,075 |
Available-for-sale Securities, Fair Value |  | 8,162,866 |  | 8,341,041 |  | 8,162,866 |  | 8,341,041 |  | 8,321,578 |
Available-for-sale Securities, Gross Unrealized Gain |  | 24,586 |  | 65,740 |  | 24,586 |  | 65,740 |  | 41,519 |
Available-for-sale Securities, Gross Unrealized Loss |  | (204,815) |  | (49,699) |  | (204,815) |  | (49,699) |  | (88,625) |
Available-for-Sale Securities, Other Than Temporary Impairments |  | (373) |  | 0 |  | (373) |  | 0 |  | (391) |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  | 8,343,468 |  | 8,325,000 |  | 8,343,468 |  | 8,325,000 |  | 8,369,075 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  | $ 8,162,866 |  | 8,341,041 |  | $ 8,162,866 |  | 8,341,041 |  | 8,321,578 |
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Nominal Yield |  | 2.14% |  |  |  | 2.14% |  |  |  |  |
Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Proceeds |  | $ 142,743 |  | 460,402 |  | $ 187,533 |  | 700,412 |  |  |
Available-for-sale Securities, Gross realized gains |  | 257 |  | 2,763 |  | 450 |  | 4,855 |  |  |
Available-for-sale Securities, Gross realized losses |  | (1,019) |  | (2,383) |  | (1,502) |  | (2,426) |  |  |
Available-for-sale Securities, Related federal and state income tax expense |  | (194) |  | 148 |  | (268) |  | 945 |  |  |
Available-for-sale Securities, Pledged as Collateral [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Pledged As Collateral, Amortized cost |  | 6,821,287 |  | 6,327,666 |  | 6,821,287 |  | 6,327,666 |  | 7,151,468 |
Available-for-sale Securities, Pledged As Collateral, Fair value |  | $ 6,653,875 |  | $ 6,317,623 |  | $ 6,653,875 |  | $ 6,317,623 |  | $ 7,089,346 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 532 |  | 367 |  | 532 |  | 367 |  | 534 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 5,127,395 |  | $ 3,818,331 |  | $ 5,127,395 |  | $ 3,818,331 |  | $ 3,773,942 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 1,846,965 |  | 268,886 |  | 1,846,965 |  | 268,886 |  | 2,118,360 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  | 6,974,360 |  | 4,087,217 |  | 6,974,360 |  | 4,087,217 |  | 5,892,302 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 120,246 |  | 44,025 |  | 120,246 |  | 44,025 |  | 30,648 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 84,942 |  | 5,674 |  | 84,942 |  | 5,674 |  | 58,368 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 205,188 |  | 49,699 |  | 205,188 |  | 49,699 |  | 89,016 |
Fixed Maturity Securities [Member] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost Basis |  | 12,644 |  |  |  | 12,644 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis |  | 990,041 |  |  |  | 990,041 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis |  | 1,548,520 |  |  |  | 1,548,520 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis |  | 285,332 |  |  |  | 285,332 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis |  | 2,836,537 |  |  |  | 2,836,537 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value |  | 12,621 |  |  |  | 12,621 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value |  | 971,431 |  |  |  | 971,431 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value |  | 1,512,106 |  |  |  | 1,512,106 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value |  | 278,924 |  |  |  | 278,924 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Single Maturity Date |  | $ 2,775,082 |  |  |  | $ 2,775,082 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield |  | 2.31% |  |  |  | 2.31% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield |  | 1.97% |  |  |  | 1.97% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield |  | 2.17% |  |  |  | 2.17% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield |  | 2.17% |  |  |  | 2.17% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Nominal Yield |  | 2.10% |  |  |  | 2.10% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity | [1] | 6.95 |  |  |  | 6.95 |  |  |  |  |
U.S. Treasury |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  | $ 494 |  | 1,000 |  | $ 494 |  | 1,000 |  | 1,000 |
Available-for-sale Securities, Fair Value |  | 490 |  | 998 |  | 490 |  | 998 |  | 1,000 |
Available-for-sale Securities, Gross Unrealized Gain |  | 0 |  | 0 |  | 0 |  | 0 |  | 0 |
Available-for-sale Securities, Gross Unrealized Loss |  | (4) |  | (2) |  | (4) |  | (2) |  | 0 |
Available-for-Sale Securities, Other Than Temporary Impairments |  | 0 |  | 0 |  | 0 |  | 0 |  | 0 |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost Basis |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis |  | 494 |  |  |  | 494 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis |  | 494 |  |  |  | 494 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  | 494 |  | 1,000 |  | 494 |  | 1,000 |  | 1,000 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value |  | 490 |  |  |  | 490 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Single Maturity Date |  | 490 |  |  |  | 490 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  | $ 490 |  | $ 998 |  | $ 490 |  | $ 998 |  | $ 1,000 |
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield |  | 0.00% |  |  |  | 0.00% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield |  | 1.99% |  |  |  | 1.99% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield |  | 0.00% |  |  |  | 0.00% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield |  | 0.00% |  |  |  | 0.00% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Nominal Yield |  | 1.99% |  |  |  | 1.99% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity | [1] | 1.59 |  |  |  | 1.59 |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 1 |  | 1 |  | 1 |  | 1 |  | 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 490 |  | $ 997 |  | $ 490 |  | $ 997 |  | $ 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 0 |  | 0 |  | 0 |  | 0 |  | 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  | 490 |  | 997 |  | 490 |  | 997 |  | 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 4 |  | 2 |  | 4 |  | 2 |  | 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0 |  | 0 |  | 0 |  | 0 |  | 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 4 |  | 2 |  | 4 |  | 2 |  | 0 |
Municipal and other tax-exempt securities |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  | 10,590 |  | 32,885 |  | 10,590 |  | 32,885 |  | 27,182 |
Available-for-sale Securities, Fair Value |  | 10,697 |  | 32,765 |  | 10,697 |  | 32,765 |  | 27,080 |
Available-for-sale Securities, Gross Unrealized Gain |  | 111 |  | 293 |  | 111 |  | 293 |  | 181 |
Available-for-sale Securities, Gross Unrealized Loss |  | (4) |  | (413) |  | (4) |  | (413) |  | (283) |
Available-for-Sale Securities, Other Than Temporary Impairments |  | 0 |  | 0 |  | 0 |  | 0 |  | 0 |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost Basis |  | 4,574 |  |  |  | 4,574 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis |  | 2,303 |  |  |  | 2,303 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis |  | 3,713 |  |  |  | 3,713 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis |  | 10,590 |  |  |  | 10,590 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  | 10,590 |  | 32,885 |  | 10,590 |  | 32,885 |  | 27,182 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value |  | 4,580 |  |  |  | 4,580 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value |  | 2,401 |  |  |  | 2,401 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value |  | 3,716 |  |  |  | 3,716 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Single Maturity Date |  | 10,697 |  |  |  | 10,697 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  | $ 10,697 |  | $ 32,765 |  | $ 10,697 |  | $ 32,765 |  | $ 27,080 |
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield | [2] | 3.45% |  |  |  | 3.45% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield | [2] | 6.27% |  |  |  | 6.27% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield | [2] | 0.00% |  |  |  | 0.00% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield | [2],[3] | 3.98% |  |  |  | 3.98% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Nominal Yield | [2] | 4.25% |  |  |  | 4.25% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity | [1] | 6.53 |  |  |  | 6.53 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Effective tax rate for nominal yield calculation |  | 25.00% |  |  |  | 25.00% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Number of days for interest rates to reset |  | 35 |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 10 |  | 13 |  | 10 |  | 13 |  | 19 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 4,784 |  | $ 1,957 |  | $ 4,784 |  | $ 1,957 |  | $ 12,765 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 495 |  | 4,655 |  | 495 |  | 4,655 |  | 4,802 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  | 5,279 |  | 6,612 |  | 5,279 |  | 6,612 |  | 17,567 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 3 |  | 1 |  | 3 |  | 1 |  | 18 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 1 |  | 412 |  | 1 |  | 412 |  | 265 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 4 |  | 413 |  | 4 |  | 413 |  | 283 |
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  | 2,799,953 |  | 2,788,543 |  | 2,799,953 |  | 2,788,543 |  | 2,858,885 |
Available-for-sale Securities, Fair Value |  | 2,738,451 |  | 2,782,070 |  | 2,738,451 |  | 2,782,070 |  | 2,834,961 |
Available-for-sale Securities, Gross Unrealized Gain |  | 1,815 |  | 7,804 |  | 1,815 |  | 7,804 |  | 1,963 |
Available-for-sale Securities, Gross Unrealized Loss |  | (63,317) |  | (14,277) |  | (63,317) |  | (14,277) |  | (25,887) |
Available-for-Sale Securities, Other Than Temporary Impairments |  | 0 |  | 0 |  | 0 |  | 0 |  | 0 |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost Basis |  | 8,070 |  |  |  | 8,070 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis |  | 987,244 |  |  |  | 987,244 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis |  | 1,548,520 |  |  |  | 1,548,520 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis |  | 256,119 |  |  |  | 256,119 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis |  | 2,799,953 |  |  |  | 2,799,953 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  | 2,799,953 |  | 2,788,543 |  | 2,799,953 |  | 2,788,543 |  | 2,858,885 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value |  | 8,041 |  |  |  | 8,041 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value |  | 968,540 |  |  |  | 968,540 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value |  | 1,512,106 |  |  |  | 1,512,106 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value |  | 249,764 |  |  |  | 249,764 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Single Maturity Date |  | 2,738,451 |  |  |  | 2,738,451 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  | $ 2,738,451 |  | $ 2,782,070 |  | $ 2,738,451 |  | $ 2,782,070 |  | $ 2,834,961 |
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield |  | 1.67% |  |  |  | 1.67% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield |  | 1.96% |  |  |  | 1.96% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield |  | 2.17% |  |  |  | 2.17% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield |  | 2.20% |  |  |  | 2.20% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Nominal Yield |  | 2.10% |  |  |  | 2.10% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity | [1] | 6.89 |  |  |  | 6.89 |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 211 |  | 121 |  | 211 |  | 121 |  | 185 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 1,675,839 |  | $ 1,388,406 |  | $ 1,675,839 |  | $ 1,388,406 |  | $ 1,465,703 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 554,819 |  | 78,828 |  | 554,819 |  | 78,828 |  | 652,296 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  | 2,230,658 |  | 1,467,234 |  | 2,230,658 |  | 1,467,234 |  | 2,117,999 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 42,732 |  | 12,690 |  | 42,732 |  | 12,690 |  | 11,824 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 20,585 |  | 1,587 |  | 20,585 |  | 1,587 |  | 14,063 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 63,317 |  | 14,277 |  | 63,317 |  | 14,277 |  | 25,887 |
Other debt securities |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  | 25,500 |  | 4,400 |  | 25,500 |  | 4,400 |  | 25,500 |
Available-for-sale Securities, Fair Value |  | 25,444 |  | 4,152 |  | 25,444 |  | 4,152 |  | 25,481 |
Available-for-sale Securities, Gross Unrealized Gain |  | 12 |  | 0 |  | 12 |  | 0 |  | 50 |
Available-for-sale Securities, Gross Unrealized Loss |  | (68) |  | (248) |  | (68) |  | (248) |  | (69) |
Available-for-Sale Securities, Other Than Temporary Impairments |  | 0 |  | 0 |  | 0 |  | 0 |  | 0 |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost Basis |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis |  | 25,500 |  |  |  | 25,500 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis |  | 25,500 |  |  |  | 25,500 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  | 25,500 |  | 4,400 |  | 25,500 |  | 4,400 |  | 25,500 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value |  | 0 |  |  |  | 0 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value |  | 25,444 |  |  |  | 25,444 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Single Maturity Date |  | 25,444 |  |  |  | 25,444 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  | $ 25,444 |  | $ 4,152 |  | $ 25,444 |  | $ 4,152 |  | $ 25,481 |
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield |  | 0.00% |  |  |  | 0.00% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield |  | 0.00% |  |  |  | 0.00% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield |  | 0.00% |  |  |  | 0.00% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield | [3] | 1.59% |  |  |  | 1.59% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Nominal Yield |  | 1.59% |  |  |  | 1.59% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity | [1] | 14.18 |  |  |  | 14.18 |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 2 |  | 2 |  | 2 |  | 2 |  | 2 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 0 |  | $ 0 |  | $ 0 |  | $ 0 |  | $ 19,959 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 20,434 |  | 4,152 |  | 20,434 |  | 4,152 |  | 472 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  | 20,434 |  | 4,152 |  | 20,434 |  | 4,152 |  | 20,431 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 0 |  | 0 |  | 0 |  | 0 |  | 41 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 68 |  | 248 |  | 68 |  | 248 |  | 28 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 68 |  | 248 |  | 68 |  | 248 |  | 69 |
Residential Mortgage Backed Securities [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  | 5,506,931 |  | 5,468,038 |  | 5,506,931 |  | 5,468,038 |  | 5,429,459 |
Available-for-sale Securities, Fair Value |  | 5,387,784 |  | 5,485,760 |  | 5,387,784 |  | 5,485,760 |  | 5,402,373 |
Available-for-sale Securities, Gross Unrealized Gain |  | 22,648 |  | 52,418 |  | 22,648 |  | 52,418 |  | 35,605 |
Available-for-sale Securities, Gross Unrealized Loss |  | (141,422) |  | (34,696) |  | (141,422) |  | (34,696) |  | (62,300) |
Available-for-Sale Securities, Other Than Temporary Impairments |  | (373) |  | 0 |  | (373) |  | 0 |  | (391) |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis |  | 5,506,931 |  |  |  | 5,506,931 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  | 5,506,931 |  | 5,468,038 |  | 5,506,931 |  | 5,468,038 |  | 5,429,459 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value |  | 5,387,784 |  |  |  | 5,387,784 |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  | $ 5,387,784 |  | $ 5,485,760 |  | $ 5,387,784 |  | $ 5,485,760 |  | $ 5,402,373 |
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Nominal Yield | [4] | 2.16% |  |  |  | 2.16% |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Average Expected Life of Mortgage-backed Securities |  |  |  |  |  | 4 years 110 days |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 308 |  | 139 |  | 308 |  | 139 |  | 217 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 3,446,282 |  | $ 2,425,303 |  | $ 3,446,282 |  | $ 2,425,303 |  | $ 2,274,604 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 1,271,217 |  | 180,364 |  | 1,271,217 |  | 180,364 |  | 1,458,587 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  | 4,717,499 |  | 2,605,667 |  | 4,717,499 |  | 2,605,667 |  | 3,733,191 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 77,507 |  | 31,310 |  | 77,507 |  | 31,310 |  | 18,758 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 64,288 |  | 3,386 |  | 64,288 |  | 3,386 |  | 43,933 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 141,795 |  | 34,696 |  | 141,795 |  | 34,696 |  | 62,691 |
U.S. government agency residential mortgage-backed securities |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  | 5,441,555 |  | 5,381,382 |  | 5,441,555 |  | 5,381,382 |  | 5,355,148 |
Available-for-sale Securities, Fair Value |  | 5,304,560 |  | 5,382,377 |  | 5,304,560 |  | 5,382,377 |  | 5,309,152 |
Available-for-sale Securities, Gross Unrealized Gain |  | 4,427 |  | 35,691 |  | 4,427 |  | 35,691 |  | 16,304 |
Available-for-sale Securities, Gross Unrealized Loss |  | (141,422) |  | (34,696) |  | (141,422) |  | (34,696) |  | (62,300) |
Available-for-Sale Securities, Other Than Temporary Impairments |  | 0 |  | 0 |  | 0 |  | 0 |  | 0 |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  | 5,441,555 |  | 5,381,382 |  | 5,441,555 |  | 5,381,382 |  | 5,355,148 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  | $ 5,304,560 |  | $ 5,382,377 |  | $ 5,304,560 |  | $ 5,382,377 |  | $ 5,309,152 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 300 |  | 139 |  | 300 |  | 139 |  | 209 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 3,440,873 |  | $ 2,425,303 |  | $ 3,440,873 |  | $ 2,425,303 |  | $ 2,268,706 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 1,271,217 |  | 180,364 |  | 1,271,217 |  | 180,364 |  | 1,458,587 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  | 4,712,090 |  | 2,605,667 |  | 4,712,090 |  | 2,605,667 |  | 3,727,293 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 77,134 |  | 31,310 |  | 77,134 |  | 31,310 |  | 18,367 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 64,288 |  | 3,386 |  | 64,288 |  | 3,386 |  | 43,933 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 141,422 |  | 34,696 |  | 141,422 |  | 34,696 |  | 62,300 |
U.S. government agency residential mortgage-backed securities | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  | 3,088,585 |  | 3,005,920 |  | 3,088,585 |  | 3,005,920 |  | 3,021,551 |
Available-for-sale Securities, Fair Value |  | 3,007,885 |  | 3,008,531 |  | 3,007,885 |  | 3,008,531 |  | 2,997,563 |
Available-for-sale Securities, Gross Unrealized Gain |  | 2,774 |  | 24,213 |  | 2,774 |  | 24,213 |  | 11,549 |
Available-for-sale Securities, Gross Unrealized Loss |  | (83,474) |  | (21,602) |  | (83,474) |  | (21,602) |  | (35,537) |
Available-for-Sale Securities, Other Than Temporary Impairments |  | 0 |  | 0 |  | 0 |  | 0 |  | 0 |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  | 3,088,585 |  | 3,005,920 |  | 3,088,585 |  | 3,005,920 |  | 3,021,551 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  | $ 3,007,885 |  | $ 3,008,531 |  | $ 3,007,885 |  | $ 3,008,531 |  | $ 2,997,563 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 174 |  | 75 |  | 174 |  | 75 |  | 113 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 2,049,432 |  | $ 1,381,687 |  | $ 2,049,432 |  | $ 1,381,687 |  | $ 1,203,041 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 710,962 |  | 87,371 |  | 710,962 |  | 87,371 |  | 824,029 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  | 2,760,394 |  | 1,469,058 |  | 2,760,394 |  | 1,469,058 |  | 2,027,070 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 44,860 |  | 20,288 |  | 44,860 |  | 20,288 |  | 9,618 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 38,614 |  | 1,314 |  | 38,614 |  | 1,314 |  | 25,919 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 83,474 |  | 21,602 |  | 83,474 |  | 21,602 |  | 35,537 |
U.S. government agency residential mortgage-backed securities | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  | 1,580,185 |  | 1,412,376 |  | 1,580,185 |  | 1,412,376 |  | 1,545,971 |
Available-for-sale Securities, Fair Value |  | 1,538,582 |  | 1,412,472 |  | 1,538,582 |  | 1,412,472 |  | 1,531,009 |
Available-for-sale Securities, Gross Unrealized Gain |  | 738 |  | 7,785 |  | 738 |  | 7,785 |  | 3,148 |
Available-for-sale Securities, Gross Unrealized Loss |  | (42,341) |  | (7,689) |  | (42,341) |  | (7,689) |  | (18,110) |
Available-for-Sale Securities, Other Than Temporary Impairments |  | 0 |  | 0 |  | 0 |  | 0 |  | 0 |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  | 1,580,185 |  | 1,412,376 |  | 1,580,185 |  | 1,412,376 |  | 1,545,971 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  | $ 1,538,582 |  | $ 1,412,472 |  | $ 1,538,582 |  | $ 1,412,472 |  | $ 1,531,009 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 93 |  | 42 |  | 93 |  | 42 |  | 69 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 1,116,337 |  | $ 731,853 |  | $ 1,116,337 |  | $ 731,853 |  | $ 863,778 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 339,515 |  | 16,388 |  | 339,515 |  | 16,388 |  | 385,816 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  | 1,455,852 |  | 748,241 |  | 1,455,852 |  | 748,241 |  | 1,249,594 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 26,663 |  | 7,213 |  | 26,663 |  | 7,213 |  | 7,297 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 15,678 |  | 476 |  | 15,678 |  | 476 |  | 10,813 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 42,341 |  | 7,689 |  | 42,341 |  | 7,689 |  | 18,110 |
U.S. government agency residential mortgage-backed securities | Government National Mortgage Association Certificates and Obligations (GNMA) [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  | 772,785 |  | 938,086 |  | 772,785 |  | 938,086 |  | 787,626 |
Available-for-sale Securities, Fair Value |  | 758,093 |  | 936,365 |  | 758,093 |  | 936,365 |  | 780,580 |
Available-for-sale Securities, Gross Unrealized Gain |  | 915 |  | 3,641 |  | 915 |  | 3,641 |  | 1,607 |
Available-for-sale Securities, Gross Unrealized Loss |  | (15,607) |  | (5,362) |  | (15,607) |  | (5,362) |  | (8,653) |
Available-for-Sale Securities, Other Than Temporary Impairments |  | 0 |  | 0 |  | 0 |  | 0 |  | 0 |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  | 772,785 |  | 938,086 |  | 772,785 |  | 938,086 |  | 787,626 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  | $ 758,093 |  | $ 936,365 |  | $ 758,093 |  | $ 936,365 |  | $ 780,580 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 33 |  | 21 |  | 33 |  | 21 |  | 27 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 275,104 |  | $ 291,806 |  | $ 275,104 |  | $ 291,806 |  | $ 201,887 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 220,740 |  | 76,605 |  | 220,740 |  | 76,605 |  | 248,742 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  | 495,844 |  | 368,411 |  | 495,844 |  | 368,411 |  | 450,629 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 5,611 |  | 3,766 |  | 5,611 |  | 3,766 |  | 1,452 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 9,996 |  | 1,596 |  | 9,996 |  | 1,596 |  | 7,201 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 15,607 |  | 5,362 |  | 15,607 |  | 5,362 |  | 8,653 |
U.S. government agency residential mortgage-backed securities | Other |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  |  |  | 25,000 |  |  |  | 25,000 |  |  |
Available-for-sale Securities, Fair Value |  |  |  | 25,009 |  |  |  | 25,009 |  |  |
Available-for-sale Securities, Gross Unrealized Gain |  |  |  | 52 |  |  |  | 52 |  |  |
Available-for-sale Securities, Gross Unrealized Loss |  |  |  | (43) |  |  |  | (43) |  |  |
Available-for-Sale Securities, Other Than Temporary Impairments |  |  |  | 0 |  |  |  | 0 |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  |  |  | 25,000 |  |  |  | 25,000 |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  |  |  | $ 25,009 |  |  |  | $ 25,009 |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  |  |  | 1 |  |  |  | 1 |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  |  |  | $ 19,957 |  |  |  | $ 19,957 |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  |  |  | 0 |  |  |  | 0 |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  |  |  | 19,957 |  |  |  | 19,957 |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  |  |  | 43 |  |  |  | 43 |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  |  |  | 0 |  |  |  | 0 |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  |  |  | 43 |  |  |  | 43 |  |  |
Privately issued residential mortgage-backed securities |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  | 65,376 |  | 86,656 |  | 65,376 |  | 86,656 |  | 74,311 |
Available-for-sale Securities, Fair Value |  | 83,224 |  | 103,383 |  | 83,224 |  | 103,383 |  | 93,221 |
Available-for-sale Securities, Gross Unrealized Gain |  | 18,221 |  | 16,727 |  | 18,221 |  | 16,727 |  | 19,301 |
Available-for-sale Securities, Gross Unrealized Loss |  | 0 |  | 0 |  | 0 |  | 0 |  | 0 |
Available-for-Sale Securities, Other Than Temporary Impairments |  | (373) |  | 0 |  | (373) |  | 0 |  | (391) |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  | 65,376 |  | 86,656 |  | 65,376 |  | 86,656 |  | 74,311 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  | $ 83,224 |  | $ 103,383 |  | $ 83,224 |  | $ 103,383 |  | $ 93,221 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  | 8 | [5] | 0 | [6] | 8 | [5] | 0 | [6] | 8 | [7]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | $ 5,409 | [5] | $ 0 | [6] | $ 5,409 | [5] | $ 0 | [6] | $ 5,898 | [7]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 0 | [5] | 0 | [6] | 0 | [5] | 0 | [6] | 0 | [7]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  | 5,409 | [5] | 0 | [6] | 5,409 | [5] | 0 | [6] | 5,898 | [7]
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 373 | [5] | 0 | [6] | 373 | [5] | 0 | [6] | 391 | [7]
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0 | [5] | 0 | [6] | 0 | [5] | 0 | [6] | 0 | [7]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | $ 373 | [5] | 0 | [6] | $ 373 | [5] | 0 | [6] | 391 | [7]
Perpetual preferred stock |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  |  |  | 12,562 |  |  |  | 12,562 |  | 12,562 |
Available-for-sale Securities, Fair Value |  |  |  | 16,568 |  |  |  | 16,568 |  | 15,767 |
Available-for-sale Securities, Gross Unrealized Gain |  |  |  | 4,006 |  |  |  | 4,006 |  | 3,205 |
Available-for-sale Securities, Gross Unrealized Loss |  |  |  | 0 |  |  |  | 0 |  | 0 |
Available-for-Sale Securities, Other Than Temporary Impairments |  |  |  | 0 |  |  |  | 0 |  | 0 |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  |  |  | 12,562 |  |  |  | 12,562 |  | 12,562 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  |  |  | $ 16,568 |  |  |  | $ 16,568 |  | $ 15,767 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  |  |  | 0 |  |  |  | 0 |  | 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  |  |  | $ 0 |  |  |  | $ 0 |  | $ 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  |  |  | 0 |  |  |  | 0 |  | 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  |  |  | 0 |  |  |  | 0 |  | 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  |  |  | 0 |  |  |  | 0 |  | 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  |  |  | 0 |  |  |  | 0 |  | 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  |  |  | 0 |  |  |  | 0 |  | 0 |
Equity securities and mutual funds |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Amortized Cost |  |  |  | 17,572 |  |  |  | 17,572 |  | 14,487 |
Available-for-sale Securities, Fair Value |  |  |  | 18,728 |  |  |  | 18,728 |  | 14,916 |
Available-for-sale Securities, Gross Unrealized Gain |  |  |  | 1,219 |  |  |  | 1,219 |  | 515 |
Available-for-sale Securities, Gross Unrealized Loss |  |  |  | (63) |  |  |  | (63) |  | (86) |
Available-for-Sale Securities, Other Than Temporary Impairments |  |  |  | 0 |  |  |  | 0 |  | 0 |
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost |  |  |  | 17,572 |  |  |  | 17,572 |  | 14,487 |
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Debt Maturities, Fair Value |  |  |  | $ 18,728 |  |  |  | $ 18,728 |  | $ 14,916 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |  |  |  | 91 |  |  |  | 91 |  | 111 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  |  |  | $ 1,668 |  |  |  | $ 1,668 |  | $ 911 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  |  |  | 887 |  |  |  | 887 |  | 2,203 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  |  |  | 2,555 |  |  |  | 2,555 |  | 3,114 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  |  |  | 22 |  |  |  | 22 |  | 7 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  |  |  | 41 |  |  |  | 41 |  | 79 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  |  |  | $ 63 |  |  |  | $ 63 |  | $ 86 |
[1] | Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without penalty.
[2] | Calculated on a taxable equivalent basis using a 25 percent effective tax rate.
[3] | Nominal yield on municipal and other tax-exempt securities and other debt securities with contractual maturity dates over ten years are based on variable rates which generally are reset within 35.
[4] | The nominal yield on mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary –– Unaudited following for current yields on available for sale securities portfolio.
[5] | Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.
[6] | Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.
[7] | Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.

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