Benefit Plans (Details 5)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Astoria Bank | Pension benefits
Assumptions used to determine net periodic cost
Discount rate (as a percent)	4.66%	3.77%
Expected return on plan assets (as a percent)	8.00%	8.00%
Astoria Bank | Excess and supplemental benefit plans
Assumptions used to determine net periodic cost
Discount rate (as a percent)	4.39%	3.49%
Astoria Bank | Directors' retirement plan
Assumptions used to determine net periodic cost
Discount rate (as a percent)	4.23%	3.21%
Astoria Bank | Retiree health care plan
Assumptions used to determine net periodic cost
Discount rate (as a percent)	4.80%	3.98%
Greater | Directors' retirement plan
Assumptions used to determine net periodic cost
Discount rate (as a percent)	3.64%	2.77%
LIB | Directors' retirement plan
Assumptions used to determine net periodic cost
Discount rate (as a percent)	0.50%	0.63%