Operations and Significant Accounting Policies (Earnings Per Share) (Details) (USD $)	0 Months Ended	3 Months Ended								12 Months Ended
	Feb. 29, 2012	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share [Abstract]
Net income		$ 10,897,000	$ 9,320,000	$ 10,296,000	$ 9,968,000	$ (25,134,000)	$ 8,211,000	$ 8,680,000	$ 8,995,000	$ 40,481,000	$ 752,000	$ 30,346,000
Basic-weighted average shares outstanding										28,301,000	28,246,000	28,715,000
Effect of dilutive potential securities										352,000	387,000	196,000
Diluted-weighted average shares outstanding										28,653,000	28,633,000	28,911,000
Basic EPS (per share)		$ 0.38	$ 0.33	$ 0.36	$ 0.36	$ (0.90)	$ 0.29	$ 0.31	$ 0.32	$ 1.43	$ 0.03	$ 1.06
Diluted EPS (per share)		$ 0.38	$ 0.32	$ 0.36	$ 0.35	$ (0.90)	$ 0.29	$ 0.30	$ 0.31	$ 1.41	$ 0.03	$ 1.05
Shares excluded from computation of earnings per share										400,000	700,000	1,500,000
Dividends per share of common stock	$ 0.15									$ 0.60	$ 0.00	$ 0.00
Dividends paid			4,300,000	4,300,000	4,300,000
Dividends payable		$ 4,256,000				$ 0				$ 4,256,000	$ 0	$ 0