Earnings Per Share (details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 1,071	$ 2,126	$ 38,955	$ 39,765
Average common shares outstanding - basic	27,139,000	26,958,000	27,116,000	26,943,000
Additional shares for stock based compensation plans	43,000	41,000	42,000	48,000
Average common shares outstanding - diluted	27,182,000	26,999,000	27,158,000	26,991,000
Earnings per share of common stock - basic	$ 0.04	$ 0.08	$ 1.44	$ 1.48
Earnings per share of common stock - diluted	$ 0.04	$ 0.08	$ 1.43	$ 1.47
Earnings Per Share, Diluted, Other Disclosures [Abstract]
Antidilutive Shares Excluded from Net Income Per Diluted Common Share Calculation	39,000	43,000	28,000	28,000