Borrowings - Long-Term Borrowings (Details) $ in Thousands, ¥ in Billions	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 JPY (¥)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 16, 2017 USD ($)	Dec. 31, 2016 JPY (¥)	Dec. 31, 2016 USD ($)	Jul. 25, 2016 JPY (¥)	Jun. 25, 2016 USD ($)
Long-Term Borrowings
Repayments of long-term debt	$ 256,473	$ 3,825	$ 2,914
Discount					$ 1,438				$ 1,350
Debt Issue Cost Related To Debt Refinancing	10,460	5,579
Outstanding principal amount					1,431,059
Interest expense	$ 64,107	28,327	29,254
Reconciliation of senior secured credit facility
Outstanding principal					1,431,059
Discount					(1,438)				(1,350)
Long term borrowings					1,388,548				$ 564,957
Aggregate future required minimum principal payments based on the terms of loan
2020					31,059
2021 and thereafter					1,400,000
Total principal of long-term borrowings					1,431,059
LIBOR rate
Long-Term Borrowings
Interest rate added to variable rate (as a percent)	1.25%
Revolving credit facility
Long-Term Borrowings
Interest rate (as a percent)								5.50%	5.50%
Outstanding principal amount					7,000
Interest expense	$ 19
Deferred financing fees					4,117
Reconciliation of senior secured credit facility
Interest rate (as a percent)								5.50%	5.50%
Outstanding principal					7,000
Net deferred financing fees					(4,117)
Long term borrowings					2,883
Aggregate future required minimum principal payments based on the terms of loan
Total principal of long-term borrowings					$ 7,000
Broker-Dealer Credit Facility on committed basis
Long-Term Borrowings
Interest expense	33	41	$ 15
Senior Secured Second Lien Notes
Long-Term Borrowings
Face amount							$ 500,000
Interest rate (as a percent)							6.75%
Reconciliation of senior secured credit facility
Interest rate (as a percent)							6.75%
Senior Secured Credit Facility
Long-Term Borrowings
Interest rate (as a percent)								4.25%	4.25%
Discount									$ 956
Outstanding principal amount									540,000
Deferred financing fees									$ 3,941
Reconciliation of senior secured credit facility
Interest rate (as a percent)								4.25%	4.25%
Outstanding principal									$ 540,000
Discount									(956)
Net deferred financing fees									(3,941)
Long term borrowings									535,103
Aggregate future required minimum principal payments based on the terms of loan
Total principal of long-term borrowings									540,000
Senior Secured Credit Facility Fourth Amendment
Long-Term Borrowings
Interest rate (as a percent)				5.13%	5.13%
Repayments of long-term debt	250,000
Discount					$ 999
Accelerated unamortized financing costs	10,500
Outstanding principal amount					900,000	$ 1,150
Deferred financing fees					$ 18,504
Reconciliation of senior secured credit facility
Interest rate (as a percent)				5.13%	5.13%
Outstanding principal					$ 900,000	1,150
Discount					(999)
Net deferred financing fees					(18,504)
Long term borrowings					880,497
Aggregate future required minimum principal payments based on the terms of loan
Total principal of long-term borrowings					$ 900,000	1,150
Senior Secured Credit Facility Fourth Amendment | Senior Secured Second Lien Notes
Long-Term Borrowings
Interest rate (as a percent)				6.75%	6.75%
Outstanding principal amount					$ 500,000
Deferred financing fees					$ 22,961
Reconciliation of senior secured credit facility
Interest rate (as a percent)				6.75%	6.75%
Outstanding principal					$ 500,000
Net deferred financing fees					(22,961)
Long term borrowings					477,039
Aggregate future required minimum principal payments based on the terms of loan
Total principal of long-term borrowings					500,000
Total Long-term borrowings
Long-Term Borrowings
Discount					999				956
Outstanding principal amount					1,431,059				569,925
Deferred financing fees					41,512				4,012
Reconciliation of senior secured credit facility
Outstanding principal					1,431,059				569,925
Discount					(999)				(956)
Net deferred financing fees					(41,512)				(4,012)
Long term borrowings					1,388,548				564,957
Aggregate future required minimum principal payments based on the terms of loan
Total principal of long-term borrowings					$ 1,431,059				$ 569,925
SBI Bonds
Long-Term Borrowings
Interest rate (as a percent)				5.00%	5.00%			5.00%	5.00%
Outstanding principal amount					$ 31,059				$ 29,925
Deferred financing fees					$ 47				$ 71
Reconciliation of senior secured credit facility
Interest rate (as a percent)				5.00%	5.00%			5.00%	5.00%
Outstanding principal					$ 31,059				$ 29,925
Net deferred financing fees					(47)				(71)
Long term borrowings					31,012				29,854
Aggregate future required minimum principal payments based on the terms of loan
Total principal of long-term borrowings					31,059				29,925
VFH | Senior Secured Credit Facility
Long-Term Borrowings
Face amount						$ 100,000
VFH | SBI Bonds
Long-Term Borrowings
Face amount										¥ 3.5	$ 33,100
Loss due to change in currency rates	$ 1,100	$ 3,200
Outstanding principal amount				¥ 3.5	31,000			¥ 3.5	29,900
Reconciliation of senior secured credit facility
Outstanding principal				3.5	31,000			3.5	29,900
Aggregate future required minimum principal payments based on the terms of loan
Total principal of long-term borrowings				¥ 3.5	$ 31,000			¥ 3.5	$ 29,900