Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning of year		$ 1,970	$ 2,519	$ 2,768
Additions for tax positions taken in prior years	$ 2,700	38	21	1
Reductions for tax positions taken in prior years		(5)	(523)	(426)
Additions for tax positions related to the current year		211	83	43
Other		(9)	0	133
Lapses of statutes of limitations		(11)	(130)	0
Unrecognized tax benefits, end of year		2,194	1,970	2,519
Unrecognized tax benefits that would impact effective tax rate, if recognized		2,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense		300	(1,900)	$ 500
Cumulative liability for interest and penalties related to uncertain tax positions		1,000	$ 700
Previously unrecognized tax benefit likely to be recognized within the next 12 months		$ 800