Debt, Debt Facilities (Details) $ in Thousands, ¥ in Billions	9 Months Ended
	Sep. 30, 2018 USD ($)		Sep. 30, 2018 JPY (¥)	Apr. 18, 2018 USD ($)	Dec. 31, 2017 USD ($)		Dec. 31, 2017 JPY (¥)		Jun. 16, 2016 USD ($)	Oct. 09, 2014 USD ($)	Oct. 09, 2014 JPY (¥)
Debt [Abstract]
Current portion of debt	$ 82,455				$ 77,840
Unamortized debt issuance costs	4,200				4,000
Unamortized debt discount					9,100
October 2014 Credit Agreement Term Loan Facility [Member]
Debt [Abstract]
Original principal amount	127,500									$ 127,500
Balance	$ 0				94,800	[1]
Interest rate	Variable 30 day: 4.627%
Interest rate	4.627%		4.627%
Term of variable rate	30 days
Repayment terms	Principal amount was paid in full during April 2018.
Term of loan	5 years
Current portion of debt	$ 20,000
October 2014 Credit Agreement Japanese Yen Term Loan Facility [Member]
Debt [Abstract]
Original principal amount | ¥			¥ 6.6								¥ 6.6
Balance	$ 0		¥ 0.0		43,500	[1]	¥ 4.9	[1]
Interest rate	Variable 30 day: 2.7595%
Interest rate	2.7595%		2.7595%
Term of variable rate	30 days
Repayment terms	Principal amount was paid in full during April 2018.
Term of loan	5 years
October 2014 Credit Agreement Revolving Credit Facility [Member]
Debt [Abstract]
Balance	$ 0				47,500	[1]
Interest rate	Variable 30 day: 4.594%
Interest rate	4.594%		4.594%
Term of variable rate	30 days
Repayment terms	Principal amount was paid in full during April 2018 and credit line was closed.
Term of loan	5 years
April 2018 Credit Agreement Term Loan Facility [Member]
Debt [Abstract]
Original principal amount	$ 400,000			$ 400,000
Balance	$ 390,000	[1],[2]			0
Interest rate	Variable 30 day: 4.49%
Interest rate	4.49%		4.49%
Term of variable rate	30 days
Repayment terms	35% of the principal amount is payable in increasing quarterly installments over a five-year period that began on June 30, 2018, with the remainder payable at the end of the five-year term.
Percentage of principal payable in installments	35.00%
Frequency of payment	Quarterly
Term of loan	5 years
April 2018 Credit Agreement Revolving Credit Facility [Member]
Debt [Abstract]
Balance	$ 62,500	[1],[2]			0
Interest rate	Variable 30 day: 4.49%
Interest rate	4.49%		4.49%
Term of variable rate	30 days
Repayment terms	Revolving line of credit expires April 18, 2023.
Term of loan	5 years
Japan Subsidiary Loan [Member]
Debt [Abstract]
Original principal amount | ¥			¥ 2.1
Balance	$ 0		¥ 0.0		5,900		¥ 0.7
Interest rate	0.66%		0.66%
Repayment terms	Principal amount was paid in full during July 2018.
Convertible Note [Member]
Debt [Abstract]
Original principal amount	$ 210,000								$ 210,000
Balance	$ 0				210,000	[1]
Interest rate	7.10%		7.10%
Interest rate	4.75%		4.75%
Repayment terms	Principal amount was paid in full during April 2018.
Unamortized debt discount and debt issuance costs					11,100
Credit Agreement [Member]
Debt [Abstract]
Unamortized debt discount and debt issuance costs					$ 2,000

[1] The carrying value of the debt reflects the amounts stated in the above table less debt issuance costs of $4.2 million as of September 30, 2018 related to the credit agreement; and a debt discount of $9.1 million and debt issuance costs of $4.0 million (consisting of $11.1 million related to the Convertible Note and $2.0 million related to the credit agreement) as of December 31, 2017, which is not reflected in this table.

[2] As of September 30, 2018, the current portion of the Company's debt (i.e. becoming due in the next 12 months) included $20.0 million of the balance of its U.S. dollar denominated debt under the New Credit Agreement facility. The Company has classified the $62.5 million borrowed under the revolving line of credit as short-term debt because it is the Company's intention to use the line of credit to borrow and pay back funds over short periods of time.