Accounting Policies - Components of Other Comprehensive Income Loss and Related Tax Impact (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax	$ (24,241)	$ 36,809	$ 8,433
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	(5,090)	12,884	2,952
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	(19,151)	23,925	5,481
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(16,580)	24,077	55,062
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(9,576)	(15,803)	(10,285)
Other Comprehensive Income (Loss), before Tax	(33,109)	12,729	68,889
Other Comprehensive Income (Loss), Tax	(6,953)	4,455	24,112
Other comprehensive income, net of tax	(26,156)	8,274	44,777
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	3,254	233	2,443
Other Comprehensive Income (Loss) before Reclassifications, Tax	683	81	855
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	2,571	152	1,588
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(250)	1,178	1,313
Other Comprehensive Income (Loss), before Tax	2,938	2,046	4,463
Other Comprehensive Income (Loss), Tax	617	716	1,562
Other comprehensive income, net of tax	2,321	1,330	2,901
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	(19,151)	23,925	5,481
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(4,533)	(10,917)	(9,833)
Other Comprehensive Income (Loss), before Tax	(29,980)	20,012	(6,694)
Other Comprehensive Income (Loss), Tax	(6,296)	7,004	(2,342)
Other comprehensive income, net of tax	(23,684)	13,008	(4,352)
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, before Tax	0	0	73,835
Other Comprehensive Income (Loss) before Reclassifications, Tax	0	0	25,842
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0	47,993
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(4,793)	(6,064)	(1,765)
Other Comprehensive Income (Loss), before Tax	(6,067)	(9,329)	71,120
Other Comprehensive Income (Loss), Tax	(1,274)	(3,265)	24,892
Other comprehensive income, net of tax	(4,793)	(6,064)	46,228
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	(16,845)	(15,375)
Reclassification from AOCI, Current Period, Tax	0	(5,897)	(5,381)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	10,948	9,994
Gain (Loss) on Investments [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	(89)	9
Reclassification from AOCI, Current Period, Tax	0	(31)	3
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	58	(6)
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	45	137	239
Reclassification from AOCI, Current Period, Tax	9	48	84
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(36)	(89)	(155)
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	(5,784)	0	0
Reclassification from AOCI, Current Period, Tax	(1,215)	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	4,569	0	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	(6,067)	(9,329)	(2,715)
Reclassification from AOCI, Current Period, Tax	(1,274)	(3,265)	(950)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	4,793	6,064	1,765
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	(316)	1,813	2,020
Reclassification from AOCI, Current Period, Tax	(66)	635	707
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 250	$ (1,178)	$ (1,313)