Operations and Significant Accounting Policies (Earnings Per Share) (Details) (USD $) In Thousands, except 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
Earnings Per Share [Abstract]
Net income	$ 11,339	$ 1,972	$ 10,255	$ 8,626	$ 10,227	$ 5,687	$ 9,533	$ 10,492	$ 32,192	$ 35,939	$ 40,481
Basic-weighted average shares outstanding									27,401,000	27,722,000	28,301,000
Effect of dilutive potential securities									368,000	392,000	352,000
Diluted-weighted average shares outstanding									27,769,000	28,114,000	28,653,000
Basic EPS (per share)	$ 0.41	$ 0.07	$ 0.38	$ 0.32	$ 0.37	$ 0.21	$ 0.35	$ 0.37	$ 1.17	$ 1.30	$ 1.43
Diluted EPS (per share)	$ 0.41	$ 0.07	$ 0.37	$ 0.31	$ 0.36	$ 0.20	$ 0.34	$ 0.37	$ 1.16	$ 1.28	$ 1.41
Shares excluded from computation of earnings per share									0	0	400,000