Goodwill and Other Intangible Assets - Other Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-lived Intangible Assets [Roll Forward]
Balance at the beginning of the year, gross	$ 58,959	$ 48,550	$ 47,970
Balance at the beginning of the year, accumulated amortization	32,962	28,280	24,360
Balance at the beginning of the year, net	25,997	20,270	23,610
Additions	39,017	10,409	580
Amortization expense	(7,865)	(4,682)	(3,920)
Balance at the end of the year, gross	97,976	58,959	48,550
Balance at the end of the year, accumulated amortization	40,827	32,962	28,280
Balance at the end of the year, net	$ 57,149	$ 25,997	$ 20,270
Weighted-average remaining life (in years)	8 years 4 months	7 years 6 months 20 days	7 years 5 months 9 days
Minimum
Finite-lived Intangible Assets [Roll Forward]
Estimated useful lives (in years)	2 months	7 months	9 months 6 days
Maximum
Finite-lived Intangible Assets [Roll Forward]
Estimated useful lives (in years)	9 years 3 months	9 years 3 months	10 years