Significant Accounting Policies Earnings per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Significant Accounting Policies [Abstract]
Net income	$ 21,544	$ 22,737	$ 26,472	$ 14,079	$ 15,842	$ 15,868	$ 19,138	$ 19,734	$ 84,834	$ 70,582	$ 61,541
Weighted Average Number of Shares Outstanding, Basic									87,748	85,209	85,892
Basic EPS	$ 0.25	$ 0.26	$ 0.30	$ 0.16	$ 0.18	$ 0.19	$ 0.23	$ 0.23	$ 0.97	$ 0.83	$ 0.72
Dilutive Securities, Effect on Basic Earnings Per Share, Including Options and Restrictive Stock Units											0
Incremental Common Shares Attributable to Share-based Payment Arrangements									175	232	309
Net Income (Loss) Available to Common Stockholders, Diluted									$ 84,834	$ 70,582	$ 61,541
Weighted Average Number of Shares Outstanding, Diluted									87,923	85,441	86,201
Diluted EPS	$ 0.25	$ 0.26	$ 0.30	$ 0.16	$ 0.18	$ 0.19	$ 0.23	$ 0.23	$ 0.96	$ 0.83	$ 0.71