Fair Value: - Changes in Level 3 assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Assets (Liabilities):
Balance at the beginning of the period	$ 1,010	$ 4,371
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)	$ (1,010)	(3,361)
Balance at the end of the period		$ 1,010