Bank subsidiary (Details 5) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Available-for-sale securities
Amortized cost	$ 642,909,000	$ 653,492,000
Gross unrealized gains	17,045,000	18,070,000
Gross unrealized losses	(554,000)	(204,000)
Estimated fair value	659,400,000	671,358,000
Available-for-sale Securities, Continuous Unrealized Loss Position
Gross unrealized losses, less than 12 months	(554,000)	(204,000)
Fair value, less than 12 months	78,620,000	32,269,000
Federal agency obligations
Available-for-sale securities
Amortized cost	165,402,000	168,324,000
Gross unrealized gains	2,606,000	3,167,000
Gross unrealized losses	(48,000)
Estimated fair value	167,960,000	171,491,000
Available-for-sale Securities, Continuous Unrealized Loss Position
Gross unrealized losses, less than 12 months	(48,000)
Fair value, less than 12 months	12,025,000
Mortgage-related securities - FNMA, FHLMC and GNMA
Available-for-sale securities
Amortized cost	399,784,000	407,175,000
Gross unrealized gains	10,061,000	10,412,000
Gross unrealized losses	(506,000)	(204,000)
Estimated fair value	409,339,000	417,383,000
Available-for-sale Securities, Continuous Unrealized Loss Position
Gross unrealized losses, less than 12 months	(506,000)	(204,000)
Fair value, less than 12 months	66,595,000	32,269,000
Municipal bonds
Available-for-sale securities
Amortized cost	77,723,000	77,993,000
Gross unrealized gains	4,378,000	4,491,000
Estimated fair value	$ 82,101,000	$ 82,484,000