Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
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	$ 13,813	$ 13,234
Denominator for basic earnings per common share, weighted average common shares outstanding	29,825,000	27,519,000
Weighted average common stock equivalents	212,000	122,000
Denominator for diluted earnings per common share	30,037,000	27,641,000
Basic earnings per common share (dollars per share)	$ 0.46	$ 0.48
Diluted earnings per common share (dollars per share)	$ 0.46	$ 0.48
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	259,288	457,689