Indebtedness (Schedule of Outstanding Debt) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ 3,485
Unamortized debt discount	6,373
Short-term Debt	167,000		$ 0
Long-term Debt	550,566		550,597
Finance lease liabilities	424		737
Total debt	$ 717,566		550,597
Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member]
Debt Instrument [Line Items]
Interest Rate	3.03%
Original Amount	$ 60,000
Unamortized debt issuance costs	0
Unamortized debt discount	0
Long Term Debt Excluding Debt Discount And Debt Issuance Costs	$ 60,000		60,000
One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member]
Debt Instrument [Line Items]
Interest Rate	1.56%
Original Amount	$ 25,000
Unamortized debt issuance costs	0
Unamortized debt discount	0
Long Term Debt Excluding Debt Discount And Debt Issuance Costs	$ 25,000		25,000
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member]
Debt Instrument [Line Items]
Interest Rate	1.61%
Original Amount	$ 25,000
Unamortized debt issuance costs	0
Unamortized debt discount	0
Long Term Debt Excluding Debt Discount And Debt Issuance Costs	$ 25,000		25,000
Six Point Seventy Percent Senior Notes [Member]
Debt Instrument [Line Items]
Interest Rate	6.70%
Original Amount	$ 100,000
Unamortized debt issuance costs	329
Unamortized debt discount	505
Long Term Debt Excluding Debt Discount And Debt Issuance Costs	$ 99,166		99,125
Seven Point Twenty Five Percent Senior Notes [Member]
Debt Instrument [Line Items]
Interest Rate	7.25%
Original Amount	$ 50,000
Unamortized debt issuance costs	170
Unamortized debt discount	87
Long Term Debt Excluding Debt Discount And Debt Issuance Costs	$ 49,743		49,725
Five Point Three Hundred Seventy Five Senior Notes [Member]
Debt Instrument [Line Items]
Interest Rate	5.375%
Original Amount	$ 300,000
Unamortized debt issuance costs	2,986
Unamortized debt discount	5,781
Long Term Debt Excluding Debt Discount And Debt Issuance Costs	291,233		291,010
Long-term Debt
Debt Instrument [Line Items]
Unamortized debt issuance costs	3,485
Unamortized debt discount	6,373
Long-term Debt	$ 550,566		550,597
Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member]
Debt Instrument [Line Items]
Interest Rate	0.58%
Unamortized debt issuance costs	$ 0
Unamortized debt discount	0
Short-term Debt	$ 67,000		0
Zero Point Thirty Six Percent Borrowing from FHLBNY Due November 16, 2020 [Member]
Debt Instrument [Line Items]
Interest Rate	0.36%
Unamortized debt issuance costs	$ 0
Unamortized debt discount	0
Short-term Debt	100,000		0
Short-term Debt
Debt Instrument [Line Items]
Unamortized debt issuance costs	0
Unamortized debt discount	0
Short-term Debt	$ 167,000	$ 302,000	$ 0