Federal Home Loan Bank Advances (Summary Of Advances Payable To The Federal Home Loan Bank) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Federal Home Loan Bank advances	$ 1,602,469	$ 1,827,612
Federal Home Loan Bank of Boston [Member]
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Total Outstanding	1,602,402	1,827,527
Weighted- Average Contractual Coupon Rate	0.59%	0.59%
Unamortized premiums	67	85
Federal Home Loan Bank advances	1,602,469	1,827,612
2013 [Member] | Federal Home Loan Bank of Boston [Member]
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Total Outstanding	1,100,000	1,425,000
Weighted- Average Contractual Coupon Rate	0.19%	0.34%
2016 [Member] | Federal Home Loan Bank of Boston [Member]
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Total Outstanding	145,934	145,934
Weighted- Average Contractual Coupon Rate	1.80%	1.80%
2017 [Member] | Federal Home Loan Bank of Boston [Member]
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Total Outstanding	500	500
Weighted- Average Contractual Coupon Rate	5.66%	5.66%
2018 - 2032 [Member] | Federal Home Loan Bank of Boston [Member]
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Total Outstanding	$ 355,968	$ 256,093
Weighted- Average Contractual Coupon Rate	1.32%	1.29%