Fair Value - Changes in Level 3 Assets Measured on a Recurring Basis (Details) - Level 3 - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	$ 3,525	$ 136	$ 8,132	$ 136
Total gains or losses (realized/unrealized):
Included in earnings	0	0	1	0
Included in other comprehensive income	0	(1)	0	(1)
Acquired	0	0	0	0
Sold out of Level 3	(25)	0	(25)	0
Transfers in and/or out of Level 3	0	0	(4,608)	0
Balance at the end of the period	$ 3,500	$ 135	$ 3,500	$ 135