Investments, Investments Temporarily Impaired (Details) $ in Thousands	Jun. 30, 2017 USD ($) Investment
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	18
Estimated fair value, less than 12 months of temporary impairment	$ 34,435
Unrealized losses, less than 12 months of temporary impairment	(27)
Estimated fair value, more than 12 months of temporary impairment	0
Unrealized losses, more than 12 months of temporary impairment	0
Estimated fair value, total temporary impairment	34,435
Unrealized losses, total temporary impairment	$ (27)
Corporate Debt Securities [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	17
Estimated fair value, less than 12 months of temporary impairment	$ 31,437
Unrealized losses, less than 12 months of temporary impairment	(25)
Estimated fair value, more than 12 months of temporary impairment	0
Unrealized losses, more than 12 months of temporary impairment	0
Estimated fair value, total temporary impairment	31,437
Unrealized losses, total temporary impairment	$ (25)
Other Municipal Debt Securities [Member]
Temporarily Impaired Investments [Abstract]
Number of investments | Investment	1
Estimated fair value, less than 12 months of temporary impairment	$ 2,998
Unrealized losses, less than 12 months of temporary impairment	(2)
Estimated fair value, more than 12 months of temporary impairment	0
Unrealized losses, more than 12 months of temporary impairment	0
Estimated fair value, total temporary impairment	2,998
Unrealized losses, total temporary impairment	$ (2)