Income Taxes - Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Current:
U.S. federal	$ 1,750	$ 14,409		$ 6,765
U.S. state	477	1,887		318
Non-U.S.	435	330		118
Total current	2,662	16,626		7,201
Deferred:
U.S. federal	2,235	(9,418)		8,130
U.S. state	1,059	819		1,037
Non-U.S.	(65)	53		112
Total deferred	3,229	(8,546)		9,279
Total income tax expense (benefit)	$ 5,891	$ 8,080	[1]	$ 16,480	[1]

[1] See Note 4.