Securities - Amortized cost, gross unrealized gains and losses and fair value of securities held to maturity (Details 1) (USD $) In Thousands, unless otherwise specified	6 Months Ended				12 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Held-to-maturity Securities, Unclassified [Abstract]
Amortized Cost	$ 214,947		$ 282,750		$ 244,184
Gross Unrealized Gains	11,990		17,221		16,947
Gross Unrealized Losses	242
Fair Value	226,695		299,971		261,131
State and political subdivisions
Held-to-maturity Securities, Unclassified [Abstract]
Amortized Cost	51,757		51,801		51,780
Gross Unrealized Gains	4,332		5,586		5,486
Gross Unrealized Losses	4
Fair Value	56,085		57,387		57,266
Mortgage-backed securities
Held-to-maturity Securities, Unclassified [Abstract]
Amortized Cost	163,190	[1]	230,949	[1]	192,404	[1]
Gross Unrealized Gains	7,658	[1]	11,635	[1]	11,461	[1]
Gross Unrealized Losses	238	[1]		[1]		[1]
Fair Value	$ 170,610	[1]	$ 242,584	[1]	$ 203,865	[1]

[1] All are residential type mortgage-backed securities