Consolidated Balance Sheets (Parenthetical) (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Amortized cost of available-for-sale securities	$ 370,038	$ 354,924	[1]
Fair value of held-to-maturity securities	$ 140,959	$ 140,875	[1]
Preferred stock, shares authorized	10,000,000	10,000,000	[1]
Common stock, no par value	$ 0	$ 0	[1]
Common stock, shares authorized	2,500,000,000	2,500,000,000	[1]
Common stock, shares issued	24,185,130	24,185,923	[1]
Preferred stock Series A [Member]
Preferred stock, par value (in dollars per share)	$ 10.00	$ 10.00	[1]
Preferred stock, shares issued	51,500	51,500	[1]
Preferred stock, shares outstanding	0	0	[1]
Preferred Stock Series B [Member]
Preferred stock, shares authorized	250,000	250,000	[1]
Preferred stock, par value (in dollars per share)	$ 0	$ 0	[1]
Preferred stock, shares issued	0	0	[1]
Preferred stock, shares outstanding	0	0	[1]

[1] Derived from audited consolidated financial statements