Securities (Securities available for sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,556,884	$ 1,584,703
Gross Unrealized Gains	28,881	15,849
Gross Unrealized Losses	(19,173)	(22,118)
Estimated Fair Value	1,566,592	1,578,434
Total debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,543,726	1,571,561
Gross Unrealized Gains	28,532	15,809
Gross Unrealized Losses	(19,173)	(22,074)
Estimated Fair Value	1,553,085	1,565,296
U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,943	25,847
Gross Unrealized Gains	158	22
Gross Unrealized Losses	0	(103)
Estimated Fair Value	5,101	25,766
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,226,085	1,254,452
Gross Unrealized Gains	13,776	9,134
Gross Unrealized Losses	(19,129)	(20,884)
Estimated Fair Value	1,220,732	1,242,702
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	311,883	290,522
Gross Unrealized Gains	14,583	6,547
Gross Unrealized Losses	(44)	(1,087)
Estimated Fair Value	326,422	295,982
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	815	740
Gross Unrealized Gains	15	106
Gross Unrealized Losses	0	0
Estimated Fair Value	830	846
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,158	13,142
Gross Unrealized Gains	349	40
Gross Unrealized Losses	0	(44)
Estimated Fair Value	$ 13,507	$ 13,138