Debt (Tables)

6 Months Ended

Jun. 30, 2017

Debt [Abstract]

Schedule of Long-term Debt Instruments [Table Text Block]

	June 30, 2017		December 31, 2016
	Long-term		Long-term
Senior Notes due May 2019	$	500,000	$	500,000
Senior Notes due December 2021		800,000		800,000
Total debt, gross		1,300,000		1,300,000
Unamortized debt issuance costs		(12,844)		(15,400)
Total debt, net	$	1,287,156	$	1,284,600