Consolidated Statements of Stockholders' Equity (Unaudited) (USD $) In Thousands, except Share data	Total	Common Stock	Value of Shares Held in Rabbi Trust at Cost	Deferred Compensation Obligation	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive (Loss)Income
Beginning balance at Dec. 31, 2009	$ 412,649	$ 209	$ (2,482)	$ 2,482	$ 225,088	$ 184,599	$ 2,753
Beginning balance, shares at Dec. 31, 2009		21,072,196
COMPREHENSIVE INCOME:
Net income	28,402					28,402
Change in Unrealized Gain on Securities Available For Sale, Net of Tax and Realized Gains/(Losses)							3,013
Change in Fair Value of Cash Flow Hedges, Net of Tax and Realized Gains/(Losses)							(8,590)
Amortization of Prior Service Cost, net of tax							70
Other Comprehensive Loss	(5,507)						(5,507)
TOTAL COMPREHENSIVE INCOME	22,895
DIVIDENDS DECLARED:
COMMON DIVIDEND DECLARED ($0.57 AND $0.54 PER SHARE)	(11,443)					(11,443)
PROCEEDS FROM EXERCISE OF STOCK OPTIONS, shares		27,229
PROCEEDS FROM EXERCISE OF STOCK OPTIONS	393	1				392
TAX BENEFIT RELATED TO EQUITY AWARD ACTIVITY	70				70
EQUITY BASED COMPENSATION	1,206				1,206
RESTRICTED STOCK AWARDS GRANTED, NET OF AWARDS, shares		103,843
RESTRICTED STOCK AWARDS GRANTED, NET OF AWARDS	(109)				(109)
DEFERRED COMPENSATION OBLIGATION			(150)	150
Ending balance at Sep. 30, 2010	425,661	210	(2,632)	2,632	226,255	201,950	(2,754)
Ending balance, shares at Sep. 30, 2010		21,203,268
Beginning balance at Dec. 31, 2010	436,472	210	(2,738)	2,738	226,708	210,320	(766)
Beginning balance, shares at Dec. 31, 2010	21,220,801	21,220,801
COMPREHENSIVE INCOME:
Net income	34,267					34,267
Change in Unrealized Gain on Securities Available For Sale, Net of Tax and Realized Gains/(Losses)							228
Change in Fair Value of Cash Flow Hedges, Net of Tax and Realized Gains/(Losses)							(4,152)
Amortization of Prior Service Cost, net of tax							330
Other Comprehensive Loss	(3,594)						(3,594)
TOTAL COMPREHENSIVE INCOME	30,673
DIVIDENDS DECLARED:
COMMON DIVIDEND DECLARED ($0.57 AND $0.54 PER SHARE)	(12,218)					(12,218)
PROCEEDS FROM EXERCISE OF STOCK OPTIONS, shares		164,100
PROCEEDS FROM EXERCISE OF STOCK OPTIONS	3,713	2			3,711
TAX BENEFIT RELATED TO EQUITY AWARD ACTIVITY	251				251
EQUITY BASED COMPENSATION	1,917				1,917
RESTRICTED STOCK AWARDS GRANTED, NET OF AWARDS, shares		60,495
RESTRICTED STOCK AWARDS GRANTED, NET OF AWARDS	(361)				(361)
SHARES ISSUED UNDER DIRECT STOCK PURCHASE PLAN, shares		19,713
SHARES ISSUED UNDER DIRECT STOCK PURCHASE PLAN	540				540
DEFERRED COMPENSATION OBLIGATION			(146)	146
TAX BENEFIT RELATED TO DEFERRED COMPENSATION DISTRIBUTIONS	79				79
Ending balance at Sep. 30, 2011	$ 461,066	$ 212	$ (2,884)	$ 2,884	$ 232,845	$ 232,369	$ (4,360)
Ending balance, shares at Sep. 30, 2011	21,465,109	21,465,109