General (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2018
Condensed Balance Sheet Statements, Captions [Line Items]
Potentially dilutive securities (in shares)	67,500	0	67,500	0
Common stock dividends (in dollars per share)	$ 0.6300	$ 0.6275	$ 1.2600	$ 1.2550
Deferred policy acquisition cost amortization	$ 149,706,000	$ 148,629,000	$ 306,240,000	$ 297,042,000
Advertising expenses	9,200,000	10,000,000.0	20,800,000	23,600,000
Reinsurance retention policy, excess retention, amount reinsured				717,000,000
Reinsurance policy, amount retained			40,000,000
Ceded premiums earned	12,000,000	16,000,000	26,000,000	31,000,000
Policyholder benefits and claims incurred, ceded	(15,000,000)	6,000,000	(16,000,000)	(52,000,000)
Revenue from contract with customer	4,500,000	4,200,000	9,200,000	8,400,000
Cost of goods and services sold	3,200,000	2,700,000	6,200,000	5,400,000
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	5,700,000		5,700,000		4,400,000
Capitalized contract cost, accumulated amortization	(1,000,000.0)		(1,000,000.0)		(300,000)
Capitalized contract cost, amortization expense	400,000		700,000
Shareholders' equity	1,816,815,000	1,767,962,000	1,816,815,000	1,767,962,000	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	$ 1,717,917,000	$ 1,669,315,000	$ 1,717,917,000	$ 1,669,315,000	1,700,674,000	$ 1,524,581,000	$ 1,620,799,000	$ 1,519,658,000
Retained Earnings [Member] | Cumulative Effect, Period Of Adoption, Adjustment [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Shareholders' equity					$ (2,014,000)	$ 0	$ 0	$ 0