Business Combination (Schedule of Intangible Assets Acquired) (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
	Apr. 28, 2017	Mar. 31, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Fair Value		$ 11,800	$ 11,800
Customer relationships - institutional
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life (in years)		14 years	14 years
Fair Value		$ 3,200	$ 3,200
Customer relationships - non-institutional
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life (in years)		10 years	10 years
Fair Value		$ 4,400	$ 4,400
Trademarks and trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life (in years)		10 years	10 years
Fair Value		$ 1,500	$ 1,500
Developed technology
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life (in years)		8 years	8 years
Fair Value		$ 2,700	$ 2,700
Nesscap
Acquired Finite-Lived Intangible Assets [Line Items]
Fair Value	$ 11,800
Nesscap | Customer relationships - institutional
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life (in years)	14 years
Fair Value	$ 3,200
Nesscap | Customer relationships - non-institutional
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life (in years)	10 years
Fair Value	$ 4,400
Nesscap | Trademarks and trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life (in years)	10 years
Fair Value	$ 1,500
Nesscap | Developed technology
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life (in years)	8 years
Fair Value	$ 2,700