Investments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 968,598	$ 968,598		$ 1,115,323
Securities available for sale	$ 1,005,426	1,005,426		$ 1,135,317
accumulated other comprehensive income loss available for sale securities adjustment pre tax		$ 11,500
Maximum percentage of shareholders' equity security holdings held of one issuer	10.00%	10.00%		10.00%
Securities pledged	$ 449,500	$ 449,500		$ 484,800
Mortgage-backed securities, weighted average life		3 years
Accrued interest receivable, available-for-sale securities	4,000	$ 4,000
Accrued interest receivable, held-to-maturity securities	2,400	2,400
Allowance for credit losses on held-to-maturity debt securities	645	645	$ 0
Debt Securities, Available-for-sale, Realized Gain	400
book value of securities sold available for sale	19,600	19,600
Reclassified to Held to Maturity [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	163,600	163,600
Securities available for sale	$ 175,100	$ 175,100