Income Taxes - Income Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of provision for tax from the federal rate to the effective tax rate [Abstract]
Income tax computed at statutory tax rate	$ 36,497	$ 36,089	$ 54,021
Tax exempt interest	(4,951)	(4,533)	(7,611)
Nondeductible interest expense	564	416	407
State income taxes, net	5,645	4,738	3,697
Income tax credits, net	(13,473)	(15,404)	(15,793)
Death benefit gains	(123)	(268)	(3,268)
Reversal of valuation allowance		0	(8,650)
Re-measurement of deferred tax assets		0	25,619
Other	(826)	1,231	293
Income tax provision	$ 23,333	$ 22,269	$ 48,715