Investment Securities (Maturity Schedule) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Available-for-sale Securities, Debt Maturities [Abstract]
Due in one year or less, amortized cost	$ 16,458
Due in one year or less, estimated fair value	16,551
Due after one year through five years, amortized cost	18,904
Due after one year through five years, estimated fair value	19,089
Due after five years through ten years, amortized cost	3,274
Due after five years through ten years, estimated fair value	3,234
Due after ten years, amortized cost	0
Due after ten years, estimated fair value	0
Total, amortized cost	38,636
Total, estimated fair value	38,874
Mortgage-backed securities, amortized cost	454,995
Mortgage-backed securities, estimated fair value	453,481
Total, amortized cost	493,631
Estimated fair value	492,355	564,850	[1]
Held-to-maturity Securities, Debt Maturities [Abstract]
Mortgage-backed securities, amortized cost	73,515
Mortgage-backed securities, estimated fair value	73,245
Total, amortized cost	73,515
Estimated fair value	$ 73,245

[1] Derived from audited consolidated financial statements