Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Federal tax rate, percent			35.00%
Income tax benefit from the Tax Act			$ 39,300
Income tax provision			$ 90,699	$ 111,199	$ 106,256
Actual income tax rates			28.50%	37.50%	38.10%
Unrecognized income tax benefits			$ 841	$ 3,982	$ 4,761
Unrecognized income tax benefits, if recognized, that would favorably affect the effective income tax rate				2,200
Accrued interest expense related to unrecognized income tax benefits			100	500
Interest expense related to unrecognized income tax benefits recognized			100	100
Reversal of accrued interest expense related to unrecognized income tax benefits			500	100
Unrecognized tax benefits, decrease resulting from settlements with taxing authorities	$ 3,300
Deferred tax liabilities, net			64,697	117,362
Valuation allowance for deferred tax assets			3,825	3,531
Cash and cash equivalents			467,430	464,617	$ 486,831	$ 432,056
Other Long-Term Liabilities
Operating Loss Carryforwards [Line Items]
Income tax reserve			900	4,500
Other Assets
Operating Loss Carryforwards [Line Items]
Deferred tax liabilities, net			10,000	12,900
Other Long-Term Obligations
Operating Loss Carryforwards [Line Items]
Deferred tax liabilities, net			74,700	$ 130,300
United Kingdom Subsidiary
Operating Loss Carryforwards [Line Items]
Trading losses			12,300
Cash and cash equivalents			43,300
Puerto Rico Subsidiary
Operating Loss Carryforwards [Line Items]
Cash and cash equivalents			$ 3,000
Subsequent Event | Scenario, Plan
Operating Loss Carryforwards [Line Items]
Federal tax rate, percent		21.00%