Fair Value Measurements and Derivative Instruments (Reconciliation) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Amortized cost
Within 1 year	$ 17,110
After 1 year through 5 years	7,814
After 5 years through 10 years	42,553
After 10 years	257,944
Amortized cost	325,421	$ 218,512
Estimated fair value
Within 1 year	17,152
After 1 year through 5 years	8,000
After 5 years through 10 years	42,674
After 10 years	257,968
Total	$ 325,794	$ 222,120