Long-Term Debt, Existing Credit Agreement (Details) $ in Thousands, ¥ in Billions		12 Months Ended
		Dec. 31, 2018 USD ($)	Dec. 31, 2018 JPY (¥)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 JPY (¥)	Oct. 09, 2014 USD ($)	Oct. 09, 2014 JPY (¥)
Long-term Debt [Abstract]
Outstanding balance	[1]	$ 434,455
October 2014 Credit Agreement [Member] | Maximum [Member]
Long-term Debt [Abstract]
Consolidated leverage ratio		2.25
October 2014 Credit Agreement [Member] | Minimum [Member]
Long-term Debt [Abstract]
Consolidated interest coverage ratio		3.00
October 2014 Credit Agreement Term Loan Facility [Member]
Long-term Debt [Abstract]
Original principal amount		$ 127,500				$ 127,500
Term of loan		5 years
Outstanding balance		$ 0		$ 94,800
October 2014 Credit Agreement Japanese Yen Term Loan Facility [Member]
Long-term Debt [Abstract]
Original principal amount | ¥			¥ 6.6				¥ 6.6
Term of loan		5 years
Outstanding balance		$ 0	¥ 0.0	43,500	¥ 4.9
October 2014 Credit Agreement Revolving Credit Facility [Member]
Long-term Debt [Abstract]
Borrowing capacity						$ 187,500
Term of loan		5 years
Outstanding balance		$ 0		$ 47,500

[1] The carrying value of the debt reflects the amounts stated in the above table less a debt discount of $4.0 million, which is not reflected in this table.