Net Earnings Per Share Net Earnings Per Share (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net Income (loss) Available to Common Stockholders, Basic	$ 51,413	$ 45,368	$ 93,984	$ 46,493
Weighted Average Number of Shares Outstanding, Basic	136,865	137,861	136,613	137,686
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	1,584	1,000	2,000	1,000
Weighted Average Number of Shares Outstanding, Diluted	138,449	138,993	138,266	138,832