Borrowings - Senior Secured Credit Facility (Details) - USD ($)					12 Months Ended
	Apr. 15, 2015	Nov. 08, 2013	May. 01, 2013	Jul. 08, 2011	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Credit Facilities
Discount							$ 2,925,000
Interest expense					$ 29,254,000	$ 30,894,000	24,646,000
Aggregate future required minimum principal payments based on the terms of loan
Reclassification of deferred financing fees						5,100,000
Senior Secured Credit Facility
Credit Facilities
Face amount				$ 320,000,000
Discount (as a percent)				2.00%
Issued amount				$ 313,600,000
Discount				$ 6,400,000	1,500,000	1,900,000
Percentage of the non-voting stock of the entity's domestic subsidiaries' direct foreign subsidiaries collateralized				100.00%
Percentage of the voting stock of the entity's domestic subsidiaries' direct foreign subsidiaries as collateral				65.00%
Increase in principal amount outstanding		$ 106,700,000	$ 150,000,000
Annual amortization obligation as a percentage of original principal amount				15.00%
Annual amortization obligation as a percentage of outstanding principal amount		1.00%
Outstanding principal amount		$ 510,000,000			$ 499,800,000
Reduction in incremental spread upon consummation of qualifying initial public offering (as a percent)					0.50%
Interest rate (as a percent)					5.25%
Aggregate future required minimum principal payments based on the terms of loan
2016					$ 5,100,000
2017					5,100,000
2018					5,100,000
2019 and thereafter					484,500,000
Total maturities of long-term debt		$ 510,000,000			499,800,000
Net carrying amount of deferred financing fees capitalized					4,700,000	5,100,000
Amortization expense related to the deferred financing fees					1,000,000	1,000,000	1,600,000
Accretion related to the net carrying amount of debt discount					$ 400,000	$ 400,000	$ 700,000
Senior Secured Credit Facility | Prime rate
Credit Facilities
Additional interest margin added to fixed and variable rates (as a percent)					3.00%
Senior Secured Credit Facility | Federal funds effective rate
Credit Facilities
Additional interest margin added to fixed and variable rates (as a percent)					3.00%
Senior Secured Credit Facility | Eurodollar
Credit Facilities
Additional interest margin added to fixed and variable rates (as a percent)					3.00%
Senior Secured Credit Facility | First option
Credit Facilities
Fixed interest rate base (as a percent)					2.25%
Senior Secured Credit Facility | First option | Federal funds effective rate
Credit Facilities
Interest rate added to variable rate (as a percent)					0.50%
Senior Secured Credit Facility | First option | Eurodollar
Credit Facilities
Interest rate added to variable rate (as a percent)					1.00%
Senior Secured Credit Facility | Second option
Credit Facilities
Fixed interest rate base (as a percent)					1.25%
Senior Secured Credit Facility | LIBOR rate
Credit Facilities
Additional interest margin added to fixed and variable rates (as a percent)					4.00%
Revolving credit facility
Credit Facilities
Maximum borrowing capacity	$ 100,000,000
Commitment fee (as a percent)	0.50%
Outstanding principal balance					$ 0
Interest expense					200,000
Aggregate future required minimum principal payments based on the terms of loan
Net carrying amount of deferred financing fees capitalized					700,000
Amortization expense related to the deferred financing fees					$ 200,000
Revolving credit facility | Federal funds effective rate
Credit Facilities
Interest rate added to variable rate (as a percent)	0.50%
Additional interest margin added to fixed and variable rates (as a percent)	3.00%
Revolving credit facility | Eurodollar
Credit Facilities
Interest rate added to variable rate (as a percent)	1.00%
Revolving credit facility | First option
Credit Facilities
Fixed interest rate base (as a percent)	2.25%
Additional interest margin added to fixed and variable rates (as a percent)	2.00%
Revolving credit facility | Second option
Credit Facilities
Fixed interest rate base (as a percent)	1.25%
Additional interest margin added to fixed and variable rates (as a percent)	3.00%