Investments - Realized Investment Gains (Losses) and Impairments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Realized (losses) gains on investments
Net realized investment (losses) gains	$ (2,010,000)	$ 1,334,000	$ 672,000
Other-than-temporary impairments on investments
Other-than-temporary impairments on available-for-sale securities recognized in earnings	(1,581,000)	(182,000)	(416,000)
Other-than-temporary impairments on available-for-sale securities recognized in other comprehensive income	0	0	0
Accounting Standards Update 2016-01
New Accounting Pronouncements
Cumulative effect of adopting ASU 2016-01				$ 100,000
Available-for-sale securities
Realized (losses) gains on investments
Gross realized gains	1,892,000	2,996,000	2,112,000
Gross realized losses	(3,189,000)	(1,756,000)	(2,147,000)
Net realized (losses) gains on available-for-sale securities	(1,297,000)	1,240,000	(35,000)
Equity securities
Realized (losses) gains on investments
Net losses recognized during the period	(819,000)
Less: net losses recognized on securities sold	(86,000)
Net unrealized losses recognized on securities held at reporting date	(733,000)
Common stock
Realized (losses) gains on investments
Common stock trading securities		0	707,000
Other investments
Realized (losses) gains on investments
Other	$ 106,000	$ 94,000	$ 0