Debt (Contractual Obligations) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Long-Term Debt - Principal, Total	$ 645,896
Long-Term Debt - Principal, Less than 1 year (2020)	10,951
Long-Term Debt - Principal, 1 - 3 years (2021 - 2022)	103,294
Long-Term Debt - Principal, 3 - 5 years (2023 - 2024)	365,936
Long-Term Debt - Principal, More than 5 years (after 2024)	165,715
Long-Term Debt - Fixed Interest, Total	107,674
Long-Term Debt - Fixed Interest, Less than 1 year (2020)	21,742
Long-Term Debt - Fixed Interest, 1 - 3 years (2021 - 2022)	41,975
Long-Term Debt - Fixed Interest, 3 - 5 years (2023 - 2024)	26,746
Long-Term Debt - Fixed Interest, More than 5 years (after 2024)	17,211
Long-Term Debt - Variable Interest, Total	13,633
Long-Term Debt - Variable Interest, Less than 1 year (2020)	4,544
Long-Term Debt - Variable Interest, 1 - 3 years (2021 - 2022)	9,089
Long-Term Debt - Variable Interest, 3 - 5 years (2023 - 2024)	0
Long-Term Debt - Variable Interest, More than 5 years (after 2024)	0
Unsecured revolving credit facility - Unused commitment fee, Total	1,077
Unsecured revolving credit facility - Unused commitment fee, Less than 1 year (2020)	351
Unsecured revolving credit facility - Unused commitment fee, 1 - 3 years (2021 - 2022)	702
Unsecured revolving credit facility - Unused commitment fee, 3 - 5 years (2023 - 2024)	24
Unsecured revolving credit facility - Unused commitment fee, More than 5 years (after 2024)	0
Operating Lease Obligations, Total	212	$ 185
Operating Lease Obligations, Less than 1 year (2020)	126	85
Operating Lease Obligations, 1 - 3 years (2021 - 2022)	82	100
Operating Lease Obligations, 3 - 5 years (2023 - 2024)	4	0
Operating Lease Obligations, More than 5 years (after 2024)	0	0
Related Party Rent Lease Obligation, Total	1,170	963
Related Party Rent Lease Obligation, Less than 1 year (2020)	790	441
Related Party Rent Lease Obligation, 1 - 3 years (2021 - 2022)	380	522
Related Party Rent Lease Obligation, 3 - 5 years (2023 - 2024)	0	0
Related Party Rent Lease Obligation, More than 5 years (after 2024)	0	0
Contractual Obligations, Total	769,662	1,148
Contractual Obligations, Less than 1 year (2020)	38,504	526
Contractual Obligations, 1 - 3 years (2021 - 2022)	155,522	622
Contractual Obligations, 3 - 5 years (2023 - 2024)	392,710	0
Contractual Obligations, More than 5 years (after 2024)	182,926	0
Long-term debt	$ 644,699	$ 618,205
Minimum [Member]
Debt Instrument [Line Items]
Commitment fee percentage	0.20%
Facility usage	50.00%
Maximum [Member]
Debt Instrument [Line Items]
Commitment fee percentage	0.25%
Facility usage	50.00%
Floating Rate Notes [Member]
Debt Instrument [Line Items]
Number of loans | loan	1
Long-term debt	$ 109,500
Floating Rate Notes [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.40%
Floating Rate Notes [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.90%
Floating Rate Notes [Member] | One-month LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.76%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	$ 374,500