Summary of Significant Accounting Policies (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) segment $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Mar. 31, 2020 USD ($)	Jan. 01, 2019 USD ($)
Investments
Maximum period considered for applying equity method accounting based on financial information provided by the investee		3 months
Accounts Receivable
Premiums receivable, allowance for doubtful accounts	$ 1,808	$ 1,754
Deferred Policy Acquisition Costs
Amortization expense	$ 146,573	146,955	$ 147,945
Premiums and Unearned Premiums
Term over which premiums are earned	1 year
Deferred revenue	$ 10,630	10,441
Advertising Costs
Advertising costs	2,232	2,311	2,182
Earnings per Weighted Average Common Share
Net income from continuing operations	130,710	138,211	99,601
Allocation of income for participating shares	575	636	(523)
Net income from continuing operations attributed to common shareholders	$ 131,285	$ 138,847	$ 99,078
Total weighted average common shares outstanding, including participating shares | shares	14,894,532	15,071,955	15,281,363
Less: weighted average participating shares | shares	(65,796)	(69,200)	(80,231)
Basic earnings per share denominator | shares	14,828,736	15,002,755	15,201,132
Common equivalent shares- non-vested performance stock grants | shares	96,990	116,272	136,675
Diluted earnings per share denominator | shares	14,925,726	15,119,027	15,337,807
Basic earnings per share (in dollars per share) | $ / shares	$ 8.85	$ 9.25	$ 6.52
Diluted earnings per share (in dollars per share) | $ / shares	$ 8.80	$ 9.18	6.46
Antidilutive common shares | shares	0	0
Undistributed earnings attributable to common shareholders - basic
Net income from continuing operations attributable to common shareholders -Basic | $ / shares	$ 8.85	$ 9.25	6.52
Dividends declared | $ / shares	(3.60)	(3.60)	(3.40)
Undistributed earnings | $ / shares	5.25	5.65	3.12
Undistributed earnings attributable to common shareholders - diluted
Net income from continuing operations attributable to common shareholders -Diluted | $ / shares	8.80	9.18	6.46
Dividends declared | $ / shares	(3.60)	(3.60)	(3.40)
Undistributed earnings | $ / shares	$ 5.20	$ 5.58	$ 3.06
Recent Accounting Pronouncements
Retained earnings	$ 821,743	$ 745,029
Fixed maturity securities, allowance for expected credit losses	(691)	(1,054)		$ (2,510)
Operating lease liabilities	$ 27,115	$ 31,000
Segments
Number of business segments | segment	1
Minimum
Equipment and Leasehold Improvements
Estimated useful lives	3 years
Maximum
Equipment and Leasehold Improvements
Estimated useful lives	10 years
Accounting Standards Update 2018-02 | Revision of Prior Period, Change in Accounting Principle, Adjustment
Recent Accounting Pronouncements
Retained earnings					$ 2,373
Accounting Standards Update 2016-02
Recent Accounting Pronouncements
Operating lease liabilities					$ 35,984