Earnings Per Common 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
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	$ 16,236	$ 14,203	$ 30,049	$ 27,437
Denominator for basic earnings per common share, weighted average common shares outstanding	30,068,000	27,534,000	29,947,000	27,527,000
Weighted average common stock equivalents	211,000	140,000	212,000	131,000
Denominator for diluted earnings per common share	30,279,000	27,674,000	30,159,000	27,658,000
Basic earnings per common share (dollars per share)	$ 0.54	$ 0.52	$ 1.00	$ 1.00
Diluted earnings per common share (dollars per share)	$ 0.54	$ 0.51	$ 1.00	$ 0.99
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	249,150	367,844	252,529	412,767