Accounting Policies - Components of Other Comprehensive Income Loss and Related Tax Impact (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 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	$ (12,590)	$ 3,536	$ 13,227	$ 31,863
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	(2,643)	1,238	2,777	11,152
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	(9,947)	2,298	10,450	20,711
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(7,285)	2,201	19,943	19,189
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(2,124)	(3,834)	(7,054)	(12,152)
Other Comprehensive Income (Loss), before Tax	(11,909)	(2,512)	16,316	10,826
Other Comprehensive Income (Loss), Tax	(2,500)	(879)	3,427	3,789
Other comprehensive income, net of tax	(9,409)	(1,633)	12,889	7,037
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	3,370	(150)	12,017	(2,342)
Other Comprehensive Income (Loss) before Reclassifications, Tax	708	(53)	2,524	(820)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	2,662	(97)	9,493	(1,522)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(149)	262	17	894
Other Comprehensive Income (Loss), before Tax	3,181	253	12,038	(966)
Other Comprehensive Income (Loss), Tax	668	88	2,528	(338)
Other comprehensive income, net of tax	2,513	165	9,510	(628)
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	(9,947)	2,298	10,450	20,711
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(755)	(2,875)	(3,594)	(8,177)
Other Comprehensive Income (Loss), before Tax	(13,546)	(886)	8,678	19,283
Other Comprehensive Income (Loss), Tax	(2,844)	(309)	1,822	6,749
Other comprehensive income, net of tax	(10,702)	(577)	6,856	12,534
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	(1,220)	(1,221)	(3,477)	(4,869)
Other Comprehensive Income (Loss), before Tax	(1,544)	(1,879)	(4,400)	(7,491)
Other Comprehensive Income (Loss), Tax	(324)	(658)	(923)	(2,622)
Other comprehensive income, net of tax	(1,220)	(1,221)	(3,477)	(4,869)
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	(4,326)	0	(12,470)
Reclassification from AOCI, Current Period, Tax	0	(1,514)	0	(4,365)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	2,812	0	8,105
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	(10)	(7)	(26)	(21)
Reclassification from AOCI, Current Period, Tax	(2)	(2)	(6)	(7)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	8	5	20	14
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	(946)	0	(4,523)	0
Reclassification from AOCI, Current Period, Tax	(199)	0	(949)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	747	0	3,574	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	(1,544)	(1,879)	(4,400)	(7,491)
Reclassification from AOCI, Current Period, Tax	(324)	(658)	(923)	(2,622)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1,220	1,221	3,477	4,869
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	(189)	403	21	1,376
Reclassification from AOCI, Current Period, Tax	(40)	141	4	482
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 149	$ (262)	$ (17)	$ (894)