Reclassification Adjustments Out of Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gain	$ (2)	$ (1)	$ (2)	$ (30)
Interest income	69,621	65,777	138,112	130,354
Other noninterest income	3,186	4,626	6,124	8,075
Salaries and employee benefits	32,754	32,931	66,341	65,372
Income tax (expense)	(10,678)	(10,257)	(18,979)	(19,988)
Net income	21,359	19,909	41,638	38,800
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassification during the period, net of tax	407	484	2,135	959
AOCI Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income			0	0
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense)	(85)	(108)	(176)	(213)
Net income	138	171	1,597	333
Gains on Available for Sale Securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gain	(2)	(1)	(2)	(30)
Amortization of Unrealized Gains and Losses Related to Securities Transfer [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	225	280	463	576
Impairment Write-Down of Equity Security [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other noninterest income			1,312	0
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense)	(166)	(199)	(332)	(398)
Net income	269	313	538	626
Amortization of Net Losses [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	435	515	870	1,030
Amortization of Prior Service Costs [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	$ 0	$ (3)	$ 0	$ (6)