Consolidated Financial Statements Consolidated Financial Statements (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
New Accounting Pronouncement, Early Adoption [Line Items]
Tax assessment reserve	$ 5,400
Net cash used in financing activities		$ (57,496)	$ (53,291)
Net cash provided by operating activities		199,489	341,837
Increase in operating expenses		30,000	15,000
Excess tax benefit, amount		3,200	1,200	$ 5,300
Proceeds from sale of finance receivables		12,100	25,800
Other income (expense), net [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Gain from foreign currency exchange		12,200
Adjustments for New Accounting Pronouncement [Member] | Retained Earnings [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Cumulative effect				$ 33,000
Accounting Standards Update 2016-09, Statutory Tax Withholding Component [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Net cash provided by operating activities		11,500	13,300
Accounting Standards Update 2016-09, Excess Tax Benefit Component [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Net cash provided by operating activities		$ 3,200	4,500
Restatement Adjustment [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Net cash used in financing activities			5,400
Net cash provided by operating activities			$ 5,400