Stockholders' Equity Share Repurchases (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 27, 2018	Jan. 31, 2016
Equity, Class of Treasury Stock [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	1,640,477	799,680	18,904
Treasury Stock, Value, Acquired, Cost Method	$ 175,000		$ 75,569
2016 Share Repurchase Plan [Member]
Equity, Class of Treasury Stock [Line Items]
Treasury Stock, Shares, Acquired			1,100,000
Treasury Stock, Value, Acquired, Cost Method			$ 75,600
Treasury Stock Acquired, Average Cost Per Share			$ 65.74
Stock Repurchase Program, Authorized Amount					$ 100,000
Stock Repurchase Program, Number of Shares Authorized to be Repurchased					5,000,000
Share Repurchase Plan [Member]
Equity, Class of Treasury Stock [Line Items]
Treasury Stock, Value, Acquired, Cost Method	$ 175,000
Stock Repurchase Program, Authorized Amount				$ 375,000
Stock Repurchase Program, Number of Shares Authorized to be Repurchased				10,000,000