EMPLOYEE BENEFIT PLANS (Details for Employee 401(k) Plan, Employee Pension Plan, Registered Retirement Savings Plan and Employee Stock Purchase Plan) - USD ($)		12 Months Ended
	Sep. 15, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee 401(k) Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of company match of employee contribution		100.00%	100.00%	100.00%
Maximum percentage of employee total compensation matched by employer (in hundredths)		4.00%	4.00%	4.00%
Company match to employee contributions		$ 9,000,000	$ 8,000,000	$ 6,000,000
Administrative expense		$ 0	$ 0	$ 0
Employee Pension Plan, London Office [Member]
Defined Contribution Plan Disclosure [Line Items]
Maximum percentage of employee total compensation matched by employer (in hundredths)		6.00%	6.00%	6.00%
Company match to employee contributions		$ 380,000	$ 420,000	$ 390,000
Registered Retirement Savings Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of company match of employee contribution		100.00%
Maximum percentage of employee total compensation matched by employer (in hundredths)		4.00%
Company match to employee contributions		$ 10,000	$ 40,000
Employee Stock Purchase Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of purchase price of company's common stock to the market price		90.00%
Increase in shares of common stock issued pursuant to stock plan (in shares)	100,000
Shares available, employee stock purchase plan		93,812	108,547
Shares of Company's common stock purchased during the period (in shares)		14,735	13,227