Securities (Securities available for sale) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,652,938	$ 1,584,703
Gross Unrealized Gains	24,512	15,849
Gross Unrealized Losses	(21,754)	(22,118)
Estimated Fair Value	1,655,696	1,578,434
Total debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,639,772	1,571,561
Gross Unrealized Gains	24,137	15,809
Gross Unrealized Losses	(21,754)	(22,074)
Estimated Fair Value	1,642,155	1,565,296
U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,830	25,847
Gross Unrealized Gains	125	22
Gross Unrealized Losses	0	(103)
Estimated Fair Value	4,955	25,766
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,281,459	1,254,452
Gross Unrealized Gains	14,401	9,134
Gross Unrealized Losses	(20,767)	(20,884)
Estimated Fair Value	1,275,093	1,242,702
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	353,483	290,522
Gross Unrealized Gains	9,611	6,547
Gross Unrealized Losses	(987)	(1,087)
Estimated Fair Value	362,107	295,982
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	740
Gross Unrealized Gains	0	106
Gross Unrealized Losses	0	0
Estimated Fair Value	0	846
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,166	13,142
Gross Unrealized Gains	375	40
Gross Unrealized Losses	0	(44)
Estimated Fair Value	$ 13,541	$ 13,138