Significant Accounting Policies Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Significant Accounting Policies [Abstract]
Net income	$ 17,015	$ 15,113	$ 23,316	$ 17,612	$ 21,544	$ 22,737	$ 26,472	$ 14,079	$ 73,056	$ 84,834	$ 70,582
Weighted Average Number of Shares Outstanding, Basic									86,974	87,748	85,209
Basic EPS	$ 0.20	$ 0.17	$ 0.27	$ 0.20	$ 0.25	$ 0.26	$ 0.30	$ 0.16	$ 0.84	$ 0.97	$ 0.83
Dilutive Securities, Effect on Basic Earnings Per Share, Including Options and Restrictive Stock Units									$ 0	$ 0	$ 0
Incremental Common Shares Attributable to Share-based Payment Arrangements									135	175	232
Net Income (Loss) Available to Common Stockholders, Diluted									$ 73,056	$ 84,834	$ 70,582
Weighted Average Number of Shares Outstanding, Diluted									87,109	87,923	85,441
Diluted EPS	$ 0.20	$ 0.17	$ 0.27	$ 0.20	$ 0.25	$ 0.26	$ 0.30	$ 0.16	$ 0.84	$ 0.96	$ 0.83