Goodwill and Intangible Assets - Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Goodwill
Gross carrying amount, beginning balance	$ 430,331	$ 238,108
Accumulated impairment, beginning balance	123,200	123,200
Net amount, beginning balance	307,131	114,908
Acquisition		192,223
Impairment	122,829
Gross carrying amount, ending balance	430,331	430,331
Accumulated impairment, ending balance	246,029	123,200
Net amount, ending balance	$ 184,302	$ 307,131
Number of trading days used in adjusted market capitalization calculation	10 days