Loans and Investments, Non-performing Loans (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan
Non-performing loans by asset class
Number of loans | loan	173	170
Carrying Value	$ 0	$ 0
Non-performing loans
Non-performing loans by asset class
Number of loans | loan	2	2
Carrying value of loans	$ 29,100	$ 29,100
Loan loss reserves	7,400	7,400
Carrying Value	36,450	36,450
Greater Than 90 Days Past Due
Non-performing loans by asset class
Past Due, Non-performing Loans	0	0
Greater Than 90 Days Past Due | Non-performing loans
Non-performing loans by asset class
Past Due, Non-performing Loans	36,450	36,450
Hotel | Non-performing loans
Non-performing loans by asset class
Carrying Value	34,750	34,750
Hotel | Greater Than 90 Days Past Due | Non-performing loans
Non-performing loans by asset class
Past Due, Non-performing Loans	34,750	34,750
Commercial | Non-performing loans
Non-performing loans by asset class
Carrying Value	1,700	1,700
Commercial | Greater Than 90 Days Past Due | Non-performing loans
Non-performing loans by asset class
Past Due, Non-performing Loans	$ 1,700	$ 1,700