Commitments, Contingencies and Guarantees - Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Minimum Rental Commitments, Capital
2018	$ 18,829
2019	17,759
2020	6,942
Total minimum lease payments	43,530
Minimum Rental Commitments, Operating
2018	33,331
2019	30,712
2020	29,238
2021	21,017
2022	18,063
Thereafter	127,723
Total minimum lease payments	260,084
Operating lease expense, net of amortization expense related to landlord incentives	13,100	$ 2,400	$ 5,300
Occupancy lease expense	12,900	1,300	3,900
Communication equipment lease expense	$ 200	$ 1,100	$ 1,400