Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net of Tax
Balance at beginning and end of period	$ 120,093	$ 263,725
Other comprehensive income (loss)
Unrealized holding gains (losses) arising during the period, net of tax	(138,435)	178,761	$ 180,441
Less: Reclassification adjustment for net gains (losses) on investments included in net income:
Net realized gains on disposals and non-credit related impairment losses	4,472	26,440	8,897
Net decrease (increase) in expected credit losses	725	(991)	0
Net unrealized gains (losses) on investments	(143,632)	153,312	171,544
Other adjustments to comprehensive income, net	0	(75)	(136)
Other comprehensive income (loss), net of tax	(143,632)	153,237	171,408
Other Comprehensive Income (Loss)
Before Tax
Balance at beginning of period	333,829	139,858	(77,114)
Other comprehensive income (loss)
Unrealized holding gains (losses) arising during the period, before tax	(175,234)	226,280	228,406
Less: Reclassification adjustment for net gains (losses) included in net income
Net realized gains on disposals and non-credit related impairment losses	5,661	33,468	11,262
Net decrease (increase) in expected credit losses	918	(1,254)
Net unrealized gains on investments	(181,813)	194,066	217,144
Other adjustments to comprehensive income, net		(95)	(172)
Other comprehensive income (loss)	(181,813)	193,971	216,972
Balance at end of period	152,016	333,829	139,858
Tax Effect
Balance at beginning of period	70,104	29,370	(16,194)
Other comprehensive income (loss)
Unrealized holding gains (losses) arising during the period, tax	(36,799)	47,519	47,965
Less: Reclassification adjustment for net gains (losses) on investments included in net income:
Net realized gains on disposals and non-credit related impairment losses	1,189	7,028	2,365
Net decrease (increase) in expected credit losses	193	(263)
Net unrealized gains on investments	(38,181)	40,754	45,600
Other adjustments to comprehensive income, net		(20)	(36)
Other comprehensive income (loss)	(38,181)	40,734	45,564
Balance at end of period	31,923	70,104	29,370
Net of Tax
Balance at beginning and end of period	120,093	263,725	110,488	$ (60,920)
Other comprehensive income (loss)
Unrealized holding gains (losses) arising during the period, net of tax	(138,435)	178,761	180,441
Less: Reclassification adjustment for net gains (losses) on investments included in net income:
Net realized gains on disposals and non-credit related impairment losses	4,472	26,440	8,897
Net decrease (increase) in expected credit losses	725	(991)
Net unrealized gains (losses) on investments	(143,632)	153,312	171,544
Other adjustments to comprehensive income, net		(75)	(136)
Other comprehensive income (loss), net of tax	$ (143,632)	$ 153,237	$ 171,408