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General (Details) - USD ($) | 3 Months Ended | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2020 | Mar. 31, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Jun. 30, 2020 | Dec. 31, 2019 | Jun. 30, 2019 | Dec. 31, 2018
Condensed Balance Sheet Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Potentially dilutive securities (in shares) | 68,000 |  | 0 | 68,000 | 0 |  |  |  |
Common stock dividends (in dollars per share) | $ 0.6300 |  | $ 0.6275 | $ 1.8900 | $ 1.8825 |  |  |  |
Deferred policy acquisition cost amortization | $ 157,365,000 |  | $ 150,929,000 | $ 463,604,000 | $ 447,971,000 |  |  |  |
Advertising expenses | 10,800,000 |  | 12,500,000 | 31,700,000 | 36,100,000 |  |  |  |
Reinsurance retention policy, excess retention, amount reinsured |  |  |  |  | 717,000,000 |  |  |  |
Reinsurance policy, amount retained |  |  |  | 40,000,000 |  |  |  |  |
Ceded premiums earned | 15,000,000 |  | 13,000,000 | 41,000,000 | 44,000,000 |  |  |  |
Policyholder benefits and claims incurred, ceded | (7,000,000) |  | 1,000,000 | (23,000,000) | (51,000,000) |  |  |  |
Revenue from contract with customer | 4,500,000 |  | 4,200,000 | 13,700,000 | 12,500,000 |  |  |  |
Cost of goods and services sold | 2,800,000 |  | 2,500,000 | 9,000,000.0 | 7,800,000 |  |  |  |
Contract with customer, asset | 0 |  |  | 0 |  |  | $ 0 |  |
Contract with customer, liability | 0 |  |  | 0 |  |  | 0 |  |
Revenue, remaining performance obligation | 0 |  |  | 0 |  |  | 0 |  |
Capitalized implementation costs for cloud computing | 5,200,000 |  |  | 5,200,000 |  |  | 4,400,000 |  |
Capitalized contract cost, accumulated amortization | (1,500,000) |  |  | (1,500,000) |  |  | (300,000) |  |
Capitalized contract cost, amortization expense | 600,000 |  |  | 1,200,000 |  |  |  |  |
Shareholders' equity | 1,900,832,000 |  | 1,802,544,000 | 1,900,832,000 | 1,802,544,000 |  | 1,799,502,000 |  |
Uncollectible or written off accrued interest receivables |  | $ 0 |  | 0 |  |  |  |  |
Accounting Standards Update 2016-13 [Member] |  |  |  |  |  |  |  |  |
Condensed Balance Sheet Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Increase (decrease) in accrued interest receivable, net |  |  |  | 0 |  |  |  |  |
Retained Earnings [Member] |  |  |  |  |  |  |  |  |
Condensed Balance Sheet Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Shareholders' equity | $ 1,801,898,000 |  | $ 1,703,861,000 | $ 1,801,898,000 | $ 1,703,861,000 | $ 1,717,917,000 | 1,700,674,000 | $ 1,669,315,000 | $ 1,519,658,000
Retained Earnings [Member] | Cumulative Effect, Period Of Adoption, Adjustment [Member] |  |  |  |  |  |  |  |  |
Condensed Balance Sheet Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Shareholders' equity |  |  |  |  |  | $ 0 | $ (2,014,000) | $ 0 | $ 0

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