Benefit Plans (Details 9)	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Astoria Federal | Pension Benefits
Assumptions used to determine net periodic cost
Discount Rate (as a percent)	4.44%	4.44%	5.39%
Expected Return on Plan Assets (as a percent)		8.00%	8.00%
Rate of Compensation Increase (as a percent)			5.10%
Astoria Federal | Excess and Supplemental Benefit Plans
Assumptions used to determine net periodic cost
Discount Rate (as a percent)	4.16%	3.99%	5.04%
Rate of Compensation Increase (as a percent)			6.10%
Astoria Federal | Directors' Retirement Plan
Assumptions used to determine net periodic cost
Discount Rate (as a percent)	4.09%	3.97%	4.71%
Rate of Compensation Increase (as a percent)			4.00%
Astoria Federal | Retiree Health Care Plan
Assumptions used to determine net periodic cost
Discount Rate (as a percent)		4.50%	5.46%
Greater | Directors' Retirement Plan
Assumptions used to determine net periodic cost
Discount Rate (as a percent)		3.78%	4.50%
LIB | Directors' Retirement Plan
Assumptions used to determine net periodic cost
Discount Rate (as a percent)		1.74%	1.90%