Investment Securities Available-for-sale Securities with Unrealized Losses (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) securities	Dec. 31, 2014 USD ($) securities
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss position less than 12 months	$ 320,460,000	$ 116,660,000
Unrealized loss less than 12 months	$ 4,018,000	$ 1,105,000
Number of securities at an unrealized loss position less than 12 months | securities	90	27
Fair value of securities in unrealized loss more than 12 months	$ 104,915,000	$ 244,021,000
Unrealized loss more than 12 months	$ 4,781,000	$ 7,675,000
Number of securities at an unrealized loss position more than 12 months | securities	38	73
Fair value of securities in unrealized loss	$ 425,375,000	$ 360,681,000
Unrealized loss	8,799,000	8,780,000
Other-than-temporary impairments	$ 0
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 less than 12 months	97.00%
Mortgage-backed securities privately issued
Available-for-sale securities that had an unrealized loss:
Number of securities at an unrealized loss position less than 12 months | securities	3
Securities in unrealized loss position with fair value less than 90% of book value | securities	2
Percentage of mortgage-backed securities in unrealized loss position for less than 12 months	3.00%
Fair value within book value	90.00%
States and political subdivisions
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss position less than 12 months	$ 7,662,000	2,602,000
Unrealized loss less than 12 months	$ 38,000	$ 12,000
Number of securities at an unrealized loss position less than 12 months | securities	8	4
Fair value of securities in unrealized loss more than 12 months	$ 213,000	$ 5,788,000
Unrealized loss more than 12 months	$ 6,000	$ 47,000
Number of securities at an unrealized loss position more than 12 months | securities	1	8
Fair value of securities in unrealized loss	$ 7,875,000	$ 8,390,000
Unrealized loss	44,000	59,000
Residential mortgage-backed securities
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss position less than 12 months	303,549,000	114,018,000
Unrealized loss less than 12 months	$ 3,902,000	$ 1,091,000
Number of securities at an unrealized loss position less than 12 months | securities	76	21
Fair value of securities in unrealized loss more than 12 months	$ 102,090,000	$ 216,224,000
Unrealized loss more than 12 months	$ 4,214,000	$ 6,773,000
Number of securities at an unrealized loss position more than 12 months | securities	33	57
Fair value of securities in unrealized loss	$ 405,639,000	$ 330,242,000
Unrealized loss	8,116,000	7,864,000
Commercial mortgage-backed securities
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss position less than 12 months	6,682,000	0
Unrealized loss less than 12 months	$ 44,000	$ 0
Number of securities at an unrealized loss position less than 12 months | securities	3	0
Fair value of securities in unrealized loss more than 12 months	$ 0	$ 19,404,000
Unrealized loss more than 12 months	$ 0	$ 286,000
Number of securities at an unrealized loss position more than 12 months | securities	0	4
Fair value of securities in unrealized loss	$ 6,682,000	$ 19,404,000
Unrealized loss	44,000	286,000
Bank-issued trust preferred securities
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss position less than 12 months	2,129,000	0
Unrealized loss less than 12 months	$ 19,000	$ 0
Number of securities at an unrealized loss position less than 12 months | securities	1	0
Fair value of securities in unrealized loss more than 12 months	$ 2,506,000	$ 2,509,000
Unrealized loss more than 12 months	$ 492,000	$ 490,000
Number of securities at an unrealized loss position more than 12 months | securities	3	3
Fair value of securities in unrealized loss	$ 4,635,000	$ 2,509,000
Unrealized loss	$ 511,000	490,000
Number of available-for-sale securities in unrealized loss position | securities	3
Equity securities
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss position less than 12 months	$ 438,000	40,000
Unrealized loss less than 12 months	$ 15,000	$ 2,000
Number of securities at an unrealized loss position less than 12 months | securities	2	2
Fair value of securities in unrealized loss more than 12 months	$ 106,000	$ 96,000
Unrealized loss more than 12 months	$ 69,000	$ 79,000
Number of securities at an unrealized loss position more than 12 months | securities	1	1
Fair value of securities in unrealized loss	$ 544,000	$ 136,000
Unrealized loss	84,000	$ 81,000
Fair Value Less Than 90 Percent of Book Value | Mortgage-backed securities privately issued
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss more than 12 months	500,000
Mortgage-backed securities in unrealized loss position for less than 12 months, aggregate book value	$ 700,000