Fair Value, Unobservable Input Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value Assets Measured on Recurring Basis Unobservable Input Reconciliation Calculation [Roll Forward]
Beginning of period balance	$ 0	$ 25,218
Total gains or losses (realized) included in income	0	406
Purchases	0	81
Settlements	0	(9,123)
Transfers into Level 3	0	144
Transfers out of Level 3	0	(16,726)
End of period balance	$ 0	$ 0