Investments (Age Analysis of Past Due Recorded Investments) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Document Period End Date	Sep. 30, 2019
Financing Receivable, Past Due	$ 21,065	$ 0
Financing Receivable, Not Past Due	5,646,289	4,983,354
Loans Receivable, Gross, Commercial, Real Estate	5,667,354	4,983,354
Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	$ 21,065	$ 0