Investments (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) security	Sep. 30, 2019 USD ($) security	Sep. 30, 2020 USD ($) security	Sep. 30, 2019 USD ($) security	Dec. 31, 2019 security
Schedule of Available-for-sale Securities [Line Items]
Gross gains on investments	$ 500,000	$ 500,000	$ 22,400,000	$ 4,900,000
Gross losses on investments	100,000	300,000	16,800,000	500,000
Proceeds from sale of investment securities	47,400,000	$ 6,000,000.0	155,000,000.0	13,000,000.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Number of Positions [Abstract]
Other-than-temporary impairment	$ 1,692,000		$ 1,692,000	0
Realized gains on sale of securities				$ 4,100,000
Number of securities sold | security		6		6
Debt Securities [Member]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Number of Positions [Abstract]
Number of debt securities with unrealized loss | security	84		84		61
Number of debt securities with unrealized loss, less than 12 months | security	68		68		41
Number of debt securities with unrealized loss, greater than 12 months | security	16		16		20