Significant Accounting Policies Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Significant Accounting Policies [Abstract]
Net income	$ 13,114	$ 12,527	$ 16,368	$ 14,377	$ 17,015	$ 15,113	$ 23,316	$ 17,612	$ 56,386	$ 73,056	$ 84,834
Weighted Average Number of Shares Outstanding, Basic									83,297	86,974	87,748
Basic EPS	$ 0.16	$ 0.15	$ 0.20	$ 0.17	$ 0.20	$ 0.17	$ 0.27	$ 0.20	$ 0.68	$ 0.84	$ 0.97
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									68	135	175
Net Income (Loss) Available to Common Stockholders, Diluted									$ 56,386	$ 73,056	$ 84,834
Weighted Average Number of Shares Outstanding, Diluted									83,365	87,109	87,923
Diluted EPS	$ 0.16	$ 0.15	$ 0.20	$ 0.17	$ 0.20	$ 0.17	$ 0.27	$ 0.20	$ 0.68	$ 0.84	$ 0.96