Investments (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 USD ($) security	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 USD ($) security	Dec. 31, 2019 security
Schedule of Available-for-sale Securities [Line Items]
Gross gains on investments	$ 1,500,000	$ 200,000	$ 21,900,000	$ 4,400,000
Gross losses on investments	1,900,000	100,000	16,700,000	200,000
Proceeds from sale of investment securities	$ 6,800,000	$ 100,000	107,600,000	7,000,000.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Number of Positions [Abstract]
Other-than-temporary impairment			$ 0	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	89		89		61
Number of debt securities with unrealized loss, less than 12 months | security	71		71		41
Number of debt securities with unrealized loss, greater than 12 months | security	18		18		20