Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Numerator [Abstract]
Net income	$ 10,209	$ 10,665	$ 34,310	$ 28,939
Basic earnings per share [Abstract]
Weighted average shares (in shares)	15,491,000	15,318,000	15,450,000	15,307,000
Diluted earnings per share [Abstract]
Effect of dilutive stock options (in shares)	64,000	21,000	51,000	24,000
Adjusted weighted average shares (in shares)	15,555,000	15,339,000	15,501,000	15,331,000
Earnings per share [Abstract]
Basic earnings per share (in dollars per share)	$ 0.66	$ 0.70	$ 2.22	$ 1.89
Diluted earnings per share (in dollars per share)	$ 0.66	$ 0.70	$ 2.21	$ 1.89
Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Options excluded from diluted calculations (in shares)	89,746	356,205	89,746	323,755