Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Amortized cost of available-for-sale securities	$ 558,818,000	$ 430,836,000
Preferred stock, shares outstanding	0
Common stock, no par value	$ 0	$ 0
Common stock, shares authorized	2,500,000,000	2,500,000,000
Common stock, shares issued	21,698,115	21,102,668
Preferred stock Series A [Member]
Preferred stock, par value	$ 10.00	$ 10.00
Preferred stock, shares authorized	200,000	200,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Preferred Stock, stated value	$ 1,000	$ 1,000
Preferred stock [Member]
Preferred stock, par value	$ 1.00	$ 1.00
Preferred stock, shares authorized	15,000,000	15,000,000
Preferred stock, shares issued	0	0