Repurchase Agreements (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
REPURCHASE AGREEMENTS [Abstract]
Repurchase Agreements, Maturities	P114D	P67D
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase agreement, balance	$ 3,580,754	$ 3,564,128
Repurchage agreement, Weighted Average Interest Rate	0.61%	0.70%
Pledged Financial Instruments, Not Separately Reported, Mortgage-Related Securities Available-for-sale or Held-for-investment	3,890,066	3,935,504
Deferred Costs	(243)	(659)
Bonds [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase agreement, balance	20,651	28,113
Repurchage agreement, Weighted Average Interest Rate	1.59%	1.64%
Pledged Financial Instruments, Not Separately Reported, Mortgage-Related Securities Available-for-sale or Held-for-investment	19,686	31,483
Residential Mortgage Backed Securities [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase agreement, balance	2,522,503	2,365,982
Repurchage agreement, Weighted Average Interest Rate	0.42%	0.48%
Pledged Financial Instruments, Not Separately Reported, Mortgage-Related Securities Available-for-sale or Held-for-investment	2,598,158	2,458,200
Residential Mortgage Backed Securities [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase agreement, balance	10,569	7,808
Repurchage agreement, Weighted Average Interest Rate	1.80%	1.84%
Pledged Financial Instruments, Not Separately Reported, Mortgage-Related Securities Available-for-sale or Held-for-investment	12,746	9,634
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase agreement, balance	246,849	248,771
Repurchage agreement, Weighted Average Interest Rate	0.39%	0.47%
Pledged Financial Instruments, Not Separately Reported, Mortgage-Related Securities Available-for-sale or Held-for-investment	306,318	291,445
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase agreement, balance	303,674	382,352
Repurchage agreement, Weighted Average Interest Rate	1.27%	1.34%
Pledged Financial Instruments, Not Separately Reported, Mortgage-Related Securities Available-for-sale or Held-for-investment	367,859	465,306
Interest-Only-Strip [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase agreement, balance	369,948	443,540
Repurchage agreement, Weighted Average Interest Rate	1.16%	1.22%
Pledged Financial Instruments, Not Separately Reported, Mortgage-Related Securities Available-for-sale or Held-for-investment	449,072	565,494
Interest-Only-Strip [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Repurchase agreement, balance	106,803	88,221
Repurchage agreement, Weighted Average Interest Rate	1.27%	1.46%
Pledged Financial Instruments, Not Separately Reported, Mortgage-Related Securities Available-for-sale or Held-for-investment	$ 136,227	$ 113,942