Securities - Unrealized Loss on Securities (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	$ 574,554	$ 412,880
More than 12 months, fair value	35,125	82,017
Total fair value	609,679	494,897
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized loss	7,525	743
More than 12 months, unrealized loss	1,027	1,147
Total unrealized loss	8,552	1,890
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	256,984	7,843
More than 12 months, fair value	62,763	109,090
Total fair value	319,747	116,933
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Less than 12 months, unrealized loss	2,871	31
More than 12 months, unrealized loss	1,740	1,214
Total unrealized loss	4,611	1,245
US Treasury
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	71,085	4,968
More than 12 months, fair value	0	0
Total fair value	71,085	4,968
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized loss	914	7
More than 12 months, unrealized loss	0	0
Total unrealized loss	914	7
US Government Agency Debentures
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	0	4,828
More than 12 months, fair value	0	0
Total fair value	0	4,828
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized loss	0	7
More than 12 months, unrealized loss	0	0
Total unrealized loss	0	7
State and Political Subdivisions
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	93,099	28,155
More than 12 months, fair value	26,796	44,269
Total fair value	119,895	72,424
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized loss	1,178	90
More than 12 months, unrealized loss	1,004	816
Total unrealized loss	2,182	906
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	119,415	7,843
More than 12 months, fair value	56,247	64,946
Total fair value	175,662	72,789
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Less than 12 months, unrealized loss	986	31
More than 12 months, unrealized loss	1,648	725
Total unrealized loss	2,634	756
Other Equity Securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	6,027	6,049
More than 12 months, fair value	0	0
Total fair value	6,027	6,049
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized loss	31	12
More than 12 months, unrealized loss	0	0
Total unrealized loss	31	12
Residential MBS
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	139,161	347,777
More than 12 months, fair value	8,329	27,632
Total fair value	147,490	375,409
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized loss	849	573
More than 12 months, unrealized loss	23	234
Total unrealized loss	872	807
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	0	0
More than 12 months, fair value	0	0
Total fair value	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Less than 12 months, unrealized loss	0	0
More than 12 months, unrealized loss	0	0
Total unrealized loss	0	0
Commercial MBS
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	265,182	21,103
More than 12 months, fair value	0	10,116
Total fair value	265,182	31,219
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized loss	4,553	54
More than 12 months, unrealized loss	0	97
Total unrealized loss	4,553	151
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	137,569	0
More than 12 months, fair value	6,516	44,144
Total fair value	144,085	44,144
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Less than 12 months, unrealized loss	1,885	0
More than 12 months, unrealized loss	92	489
Total unrealized loss	$ 1,977	$ 489