Investment Securities - Gross Unrealized Losses and Fair Values of Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012 securities	Dec. 31, 2011 securities
Available-for-Sale:
Available-for-Sale, less than 12 months fair value	$ 344,180	$ 333,344
Available-for-Sale, less than 12 months gross unrealized losses	(1,689)	(686)
Available-for-Sale, 12 months or more fair value	137	177
Available-for-sale, 12 months or more gross unrealized losses	(1)	(6)
Available-for-Sale, total fair value	344,317	333,521
Available-for-sale, total gross unrealized losses	(1,690)	(692)
Held-to-Maturity:
Held-to-maturity, less than 12 months fair value	28,701
Held-to-maturity, less than 12 months gross unrealized losses	(181)
Held-to-maturity, 12 months or more fair value	557
Held-to-maturity, 12 months or more gross unrealized losses	(8)
Held-to-maturity, total fair value	29,258
Held-to-maturity, total gross unrealized losses	(189)
Available-for-Sale and Held-to-Maturity:
Investment securities in an unrealized loss position (number of securities)	69,000	24,000
Obligations of U.S. government agencies
Available-for-Sale:
Available-for-Sale, less than 12 months fair value	93,982	287,404
Available-for-Sale, less than 12 months gross unrealized losses	(163)	(662)
Available-for-Sale, 12 months or more fair value	0	0
Available-for-sale, 12 months or more gross unrealized losses	0	0
Available-for-Sale, total fair value	93,982	287,404
Available-for-sale, total gross unrealized losses	(163)	(662)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations
Available-for-Sale:
Available-for-Sale, less than 12 months fair value	250,198	45,694
Available-for-Sale, less than 12 months gross unrealized losses	(1,526)	(14)
Available-for-Sale, 12 months or more fair value	0	0
Available-for-sale, 12 months or more gross unrealized losses	0	0
Available-for-Sale, total fair value	250,198	45,694
Available-for-sale, total gross unrealized losses	(1,526)	(14)
Private mortgage-backed securities
Available-for-Sale:
Available-for-Sale, less than 12 months fair value	0	246
Available-for-Sale, less than 12 months gross unrealized losses	0	(10)
Available-for-Sale, 12 months or more fair value	137	177
Available-for-sale, 12 months or more gross unrealized losses	(1)	(6)
Available-for-Sale, total fair value	137	423
Available-for-sale, total gross unrealized losses	(1)	(16)
State, county and municipal securities
Held-to-Maturity:
Held-to-maturity, less than 12 months fair value	19,389	0
Held-to-maturity, less than 12 months gross unrealized losses	(168)	0
Held-to-maturity, 12 months or more fair value	557	773
Held-to-maturity, 12 months or more gross unrealized losses	(8)	(17)
Held-to-maturity, total fair value	19,946	773
Held-to-maturity, total gross unrealized losses	(176)	(17)
Corporate securities
Held-to-Maturity:
Held-to-maturity, less than 12 months fair value	9,312
Held-to-maturity, less than 12 months gross unrealized losses	(13)
Held-to-maturity, 12 months or more fair value	0
Held-to-maturity, 12 months or more gross unrealized losses	0
Held-to-maturity, total fair value	9,312
Held-to-maturity, total gross unrealized losses	$ (13)