Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator and denominator of the basic and diluted earnings per common share computations
Numerator for both basic and diluted earnings per common share, net income	$ 14,993	$ 13,106	$ 42,430	$ 39,346
Denominator for basic earnings per common share, weighted average common shares outstanding	27,870,000	27,498,000	27,642,000	27,490,000
Weighted average common stock equivalents	167,000	90,000	144,000	78,000
Denominator for diluted earnings per common share	28,037,000	27,588,000	27,786,000	27,568,000
Basic earnings per common share (dollars per share)	$ 0.54	$ 0.48	$ 1.54	$ 1.43
Diluted earnings per common share (dollars per share)	$ 0.53	$ 0.48	$ 1.53	$ 1.43
Stock Option [Member]
Earnings Per Common Share (Textual) [Abstract]
Average number of exercisable employee stock option awards that were not included in the computation of diluted earnings per common share	308,009	611,605	377,847	618,703