Fair Value of Financial Instruments (Level 3 Securities) (Details) - Recurring - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 1,552	$ 1,629
Net unrealized gains (losses)	(144)	(221)
Ending Balance	1,408	1,408
Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	100	100
Net unrealized gains (losses)		0
Ending Balance	100	100
Asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	632	647
Net unrealized gains (losses)	7	(8)
Ending Balance	639	639
Equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	820	882
Net unrealized gains (losses)	(151)	(213)
Ending Balance	$ 669	$ 669