Goodwill and Intangible Assets - Estimated Future Amortization Expense by Year (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 16,100	$ 16,400	$ 13,200
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2018	13,733
2019	13,569
2020	13,496
2021	13,328
2022	$ 13,328