Goodwill and Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets

Schedule of goodwill by segment

	Market		Execution
(in thousands)	Making		Services		Corporate		Total
Balance as of December 31, 2016	$	657,985	$	57,394	$	—	$	715,379
Additions		97,307		32,197		—		129,504
Balance as of December 31, 2017	$	755,292	$	89,591	$	—	$	844,883

Schedule of acquired intangible assets

	As of December 31, 2017
	Gross
	Carrying		Accumulated		Net Carrying		Useful Lives
(in thousands)	Amount		Amortization		Amount		(Years)
Purchased technology	$	110,000	$	110,000	$	—	1.4	to	2.5
ETF issuer relationships		950		559		391		9
ETF buyer relationships		950		559		390		9
Leases		1,800		397		1,403		3
FCC licenses		200		19		181		7
Technology		60,000		9,644		50,356	1	to	6
Customer relationships		49,000		1,822		47,178	12	to	17
Favorable occupancy leases		5,895		408		5,487		7
Exchange memberships		5,838		—		5,838		Indefinite
	$	234,633	$	123,408	$	111,224

	As of December 31, 2016
	Gross
	Carrying		Accumulated		Net Carrying		Useful Lives
(in thousands)	Amount		Amortization		Amount		(Years)
Purchased technology	$	110,000	$	110,000	$	—	1.4	to	2.5
ETF issuer relationships		950		454		496		9
ETF buyer relationships		950		454		496		9
	$	111,900	$	110,908	$	992