Other Income, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other Income and Expenses [Abstract]
Interest income	$ 1,422	$ 162	$ 2,406	$ 451
Other nonoperating income	193	511	4,940	1,594
Insurance policy expense	(79)	(129)	(261)	(205)
Other Nonoperating Expense	0	0	0	(3)
Other income, net	$ 1,536	$ 544	$ 7,085	$ 1,837