Shareholders' Equity (AOCI rollforward) (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 10, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at Beginning of Period	$ 1,268,200	$ 1,231,868	$ 1,161,537
Other Comprehensive Income (Loss)	19,931	(8,851)	(809)
Balance at End of Period	1,286,832	1,268,200	1,231,868
Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at Beginning of Period	(36,010)	(27,715)	(28,892)
Other Comprehensive Income (Loss) Before Reclassification	(3,709)	(3,284)	535
Cumulative Effect of New Accounting Principle in Period of Adoption				$ 0
Amounts Reclassified from Accumulated Other Comprehensive Income	963	958	642
Other Comprehensive Income (Loss)	(2,746)	(2,326)	1,177
Reclassification of the Income Tax Effect of the Tax Reform from AOCI to RE		(5,969)
Balance at End of Period	(38,756)	(36,010)	(27,715)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at Beginning of Period	(51,043)	(34,715)	(33,906)
Other Comprehensive Income (Loss) Before Reclassification	18,459	(11,404)	(2,650)
Cumulative Effect of New Accounting Principle in Period of Adoption				0
Amounts Reclassified from Accumulated Other Comprehensive Income	1,472	2,553	1,841
Other Comprehensive Income (Loss)	19,931	(8,851)	(809)
Reclassification of the Income Tax Effect of the Tax Reform from AOCI to RE		(7,477)
Balance at End of Period	(31,112)	(51,043)	(34,715)
Available-for-sale Securities | Unrealized Gains and Losses on Net Investment Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at Beginning of Period	(10,447)	(1,915)	1,270
Other Comprehensive Income (Loss) Before Reclassification	22,168	(8,120)	(3,185)
Cumulative Effect of New Accounting Principle in Period of Adoption				(3,259)
Amounts Reclassified from Accumulated Other Comprehensive Income	(103)	0	0
Other Comprehensive Income (Loss)	18,806	(8,120)	(3,185)
Reclassification of the Income Tax Effect of the Tax Reform from AOCI to RE		(412)
Balance at End of Period	8,359	(10,447)	(1,915)
Held-to-maturity Securities | Unrealized Gains and Losses on Net Investment Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at Beginning of Period	(4,586)	(5,085)	(6,284)
Other Comprehensive Income (Loss) Before Reclassification	0	0	0
Cumulative Effect of New Accounting Principle in Period of Adoption				$ 3,259
Amounts Reclassified from Accumulated Other Comprehensive Income	612	1,595	1,199
Other Comprehensive Income (Loss)	3,871	1,595	1,199
Reclassification of the Income Tax Effect of the Tax Reform from AOCI to RE		(1,096)
Balance at End of Period	$ (715)	$ (4,586)	$ (5,085)