Investment Securities (Available-for-sale Securities with Unrealized Loss) (Details) $ in Thousands	Mar. 31, 2018 USD ($) securities	Dec. 31, 2017 USD ($) securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	$ 353,615	$ 294,746
Less than 12 months, unrealized loss	$ 7,795	$ 3,575
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities	134	97
12 months or more, fair value	$ 288,935	$ 301,298
12 months or more, unrealized loss	$ 13,347	$ 10,010
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities	92	94
Total unrealized loss position, fair value	$ 642,550	$ 596,044
Total unrealized loss	21,142	13,585
States and political subdivisions
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	26,370	16,985
Less than 12 months, unrealized loss	$ 306	$ 89
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities	37	18
12 months or more, fair value	$ 5,095	$ 5,308
12 months or more, unrealized loss	$ 271	$ 167
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities	2	1
Total unrealized loss position, fair value	$ 31,465	$ 22,293
Total unrealized loss	577	256
Residential mortgage-backed securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	321,636	274,998
Less than 12 months, unrealized loss	$ 7,396	$ 3,462
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities	95	77
12 months or more, fair value	$ 279,802	$ 291,812
12 months or more, unrealized loss	$ 12,841	$ 9,556
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities	86	88
Total unrealized loss position, fair value	$ 601,438	$ 566,810
Total unrealized loss	20,237	13,018
Commercial mortgage-backed securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	5,609	2,487
Less than 12 months, unrealized loss	$ 93	$ 23
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities	2	1
12 months or more, fair value	$ 1,256	$ 1,274
12 months or more, unrealized loss	$ 17	$ 16
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities	1	1
Total unrealized loss position, fair value	$ 6,865	$ 3,761
Total unrealized loss	110	39
Bank-issued trust preferred securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	0	0
Less than 12 months, unrealized loss	$ 0	$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities	0	0
12 months or more, fair value	$ 2,782	$ 2,792
12 months or more, unrealized loss	$ 218	$ 207
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities	3	3
Total unrealized loss position, fair value	$ 2,782	$ 2,792
Total unrealized loss	$ 218	207
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	3
Equity securities (a)
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value		276
Less than 12 months, unrealized loss		$ 1
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		1
12 months or more, fair value		$ 112
12 months or more, unrealized loss		$ 64
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities		1
Total unrealized loss position, fair value		$ 388
Total unrealized loss		$ 65
Mortgage-backed securities, issued by US government sponsored agencies
Available-for-sale securities that had an unrealized loss:
Percentage of mortgage-backed securities in unrealized loss position for more than 12 months	99.00%
Mortgage-backed securities, privately issued
Available-for-sale securities that had an unrealized loss:
Percentage of mortgage-backed securities in unrealized loss position for more than 12 months	1.00%
Number of privately issued mortgage-backed securities securities with book value less than 90% of fair value | securities	4
Fair value within book value	90.00%
Fair Value Less Than 90 Percent of Book Value [Member] | Mortgage-backed securities, privately issued
Available-for-sale securities that had an unrealized loss:
12 months or more, fair value	$ 300
Book value of privately issued mortgage-backed securities in unrealized loss position for more than 12 months	$ 500