Accounting Policies - Components of Other Comprehensive Income Loss and Related Tax Impact (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	$ 2,795	$ 9,525	$ 25,817	$ 28,328
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	586	3,334	5,421	9,915
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	2,209	6,191	20,396	18,413
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	3,987	4,691	27,227	16,987
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(2,688)	(3,807)	(4,929)	8,317
Other Comprehensive Income (Loss), before Tax	1,644	1,360	28,225	13,339
Other Comprehensive Income (Loss), Tax	345	476	5,927	4,669
Other comprehensive income, net of tax	1,299	884	22,298	8,670
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	2,251	(2,309)	8,647	(2,192)
Other Comprehensive Income (Loss) before Reclassifications, Tax	473	(809)	1,816	(766)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	1,778	(1,500)	6,831	(1,426)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	45	(299)	(166)	(633)
Other Comprehensive Income (Loss), before Tax	2,194	(1,848)	8,857	(1,219)
Other Comprehensive Income (Loss), Tax	461	(647)	1,860	(426)
Other comprehensive income, net of tax	1,733	(1,201)	6,997	(793)
Available-for-sale Securities [Member] | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	2,209	6,191	20,396	18,413
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1,421	2,725	2,838	5,302
Other Comprehensive Income (Loss), before Tax	996	5,333	22,224	20,170
Other Comprehensive Income (Loss), Tax	208	1,867	4,666	7,059
Other comprehensive income, net of tax	788	3,466	17,558	13,111
Held-to-maturity Securities [Member] | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1,222	1,381	2,257	3,648
Other Comprehensive Income (Loss), before Tax	(1,546)	(2,125)	(2,856)	(5,612)
Other Comprehensive Income (Loss), Tax	(324)	(744)	(599)	(1,964)
Other comprehensive income, net of tax	(1,222)	(1,381)	(2,257)	(3,648)
Gain (Loss) on Derivative Instruments [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Available-for-sale Securities [Member] | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	(4,186)	0	(8,145)
Reclassification from AOCI, Current Period, Tax	0	(1,465)	0	(2,851)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	2,721	0	5,294
Other Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Available-for-sale Securities [Member] | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(8)	(6)	(15)	(13)
Reclassification from AOCI, Current Period, Tax	(2)	(2)	(3)	(5)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	6	4	12	8
Interest Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Available-for-sale Securities [Member] | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(1,791)	0	(3,578)	0
Reclassification from AOCI, Current Period, Tax	(376)	0	(752)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1,415	0	2,826	0
Interest Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Held-to-maturity Securities [Member] | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(1,546)	(2,125)	(2,856)	(5,612)
Reclassification from AOCI, Current Period, Tax	(324)	(744)	(599)	(1,964)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1,222	1,381	2,257	3,648
Interest Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(57)	461	210	973
Reclassification from AOCI, Current Period, Tax	(12)	162	44	340
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 45	$ (299)	$ (166)	$ (633)