Income Taxes - Effective Income Tax Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended						6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax expense (benefit) at U.S. federal income tax rate											$ 9,706	$ 5,175	$ (7,312)
State income taxes, net of federal income tax effect											883	447	497
Federal and state deferred tax rate change											(5,119)	0	0
Transition tax											5,323	0	0
Effect of non-US operations											(2,228)	(781)	89
Nontaxable contingent liability fair value changes and goodwill impairment											237	3,578	13,083
Research and development credit											(38)	(140)	(422)
Change in valuation allowances											2,103	2,206	5,173
Prior year provision to return adjustment											(581)	(137)	(948)
Write-off of deferred taxes and tax receivables											70	193	858
Change in valuation allowances											932	293	480
Prior year provision to return adjustment	$ 3,728	$ 3,362	$ 2,354	$ 2,292	$ 2,974	$ 2,110	$ 5,716	$ 5,084	$ 9,444	$ 7,376	$ 11,288	$ 10,834	$ 11,498