Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 393,361	$ 317,885	$ 176,747
Less Than 12 Months, Gross Unrealized Losses	5,501	3,998	4,243
12 Months or More, Fair Value	142,701	302,630	341,437
12 Months or More, Gross Unrealized Losses	3,182	7,295	9,746
Total, Fair Value	536,062	620,515	518,184
Total, Gross Unrealized Losses	8,683	11,293	13,989
Government sponsored agencies [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	13,703	166,963	1,744
Less Than 12 Months, Gross Unrealized Losses	349	406	4
12 Months or More, Fair Value	13,275	31,927	24,810
12 Months or More, Gross Unrealized Losses	131	105	38
Total, Fair Value	26,978	198,890	26,554
Total, Gross Unrealized Losses	480	511	42
State and political subdivisions [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	208,376	62,310	91,532
Less Than 12 Months, Gross Unrealized Losses	4,762	3,348	4,010
12 Months or More, Fair Value	66,505	36,847	70,116
12 Months or More, Gross Unrealized Losses	2,255	1,226	2,466
Total, Fair Value	274,881	99,157	161,648
Total, Gross Unrealized Losses	7,017	4,574	6,476
Residential mortgage-backed securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	133,975	17,276	34,280
Less Than 12 Months, Gross Unrealized Losses	293	52	144
12 Months or More, Fair Value	3,567	180,194	196,045
12 Months or More, Gross Unrealized Losses	54	1,491	2,571
Total, Fair Value	137,542	197,470	230,325
Total, Gross Unrealized Losses	347	1,543	2,715
Collateralized Mortgage Obligations [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	27,643	63,077	44,195
Less Than 12 Months, Gross Unrealized Losses	36	179	81
12 Months or More, Fair Value	44,062	31,620	28,544
12 Months or More, Gross Unrealized Losses	534	1,015	1,093
Total, Fair Value	71,705	94,697	72,739
Total, Gross Unrealized Losses	570	1,194	1,174
Corporate bonds [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	9,664	0	4,996
Less Than 12 Months, Gross Unrealized Losses	61	0	4
12 Months or More, Fair Value	14,992	14,952	14,937
12 Months or More, Gross Unrealized Losses	8	48	63
Total, Fair Value	24,656	14,952	19,933
Total, Gross Unrealized Losses	69	48	67
Trust Preferred Securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	0	0	0
Less Than 12 Months, Gross Unrealized Losses	0	0	0
12 Months or More, Fair Value	300	7,090	6,985
12 Months or More, Gross Unrealized Losses	200	3,410	3,515
Total, Fair Value	300	7,090	6,985
Total, Gross Unrealized Losses	$ 200	3,410	$ 3,515
US Treasury Securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value		8,259
Less Than 12 Months, Gross Unrealized Losses		13
12 Months or More, Fair Value		0
12 Months or More, Gross Unrealized Losses		0
Total, Fair Value		8,259
Total, Gross Unrealized Losses		$ 13