Consolidated Statements of Financial Condition (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Consolidated Statements of Financial Condition [Abstract]
Securities available for sale; cost	$ 1,045,225	$ 1,065,447
Loans receivable, allowance for loan losses	$ 6,721	$ 6,709
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	30,000,000	30,000,000
Common stock, shares issued	19,214,524	19,211,434
Common stock, shares outstanding	17,618,877	17,600,334
Treasury stock, shares	1,595,647	1,611,100
Stock split ratio	six-for-five stock	six-for-five stock