Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income, Before-tax Amount	$ 547,354	$ 480,138	$ 388,451
Net income, Tax (Expense) Benefit	(118,878)	(204,664)	(141,667)
Net income	428,476	275,474	246,784
Net change related to cash flow hedges: Before-tax Amount
Reclassification adjustment for losses realized in net income, Before-tax Amount	0	130	467
Net change related to cash flow hedges: Tax (Expense) Benefit
Reclassification adjustment for losses realized in net income, Tax (Expense) Benefit	0	(50)	(180)
Net change related to cash flow hedges: Net of Tax Amount
Reclassification adjustment for losses realized in net income, Net of Tax Amount	0	80	287
Net unrealized (losses) gains on investment securities available for sale: Before-tax Amount
Reclassification adjustment for net losses (gains) realized in net income, Before-tax Amount	1,296	289	(6,011)
Net unrealized (losses) gains arising during the period, Before-tax Amount	(44,565)	1,038	(36,432)
Net unrealized (losses) gains, Before-tax Amount	(43,269)	1,327	(42,443)
Net unrealized (losses) gains on investment securities available for sale: Tax (Expense) Benefit
Reclassification adjustment for net losses (gains) realized in net income, Tax (Expense) Benefit	(336)	(111)	2,314
Net unrealized (losses) gains arising during the period, Tax (Expense) Benefit	11,542	(362)	14,027
Net unrealized (losses) gains, Tax (Expense) Benefit	11,206	(473)	16,341
Net unrealized (losses) gains on investment securities available for sale: Net of Tax Amount
Reclassification adjustment for net losses (gains) realized in net income, Net of Tax Amount	960	178	(3,697)
Net unrealized gains (losses) arising during the period, Net of Tax Amount	(33,023)	676	(22,405)
Net unrealized (losses) gains, Net of Tax Amount	(32,063)	854	(26,102)
Post-retirement unfunded health benefit: Before-tax Amount
Reclassification adjustment for gains realized in net income, Before-tax Amount	(132)	(110)	(144)
Actuarial (losses) gains arising during the period, Before-tax Amount	(46)	61	102
Net decrease in unrealized gains, net, Before-tax Amount	(178)	(49)	(42)
Post-retirement unfunded health benefit: Tax (Expense) Benefit
Reclassification adjustment for gains realized in net income, Tax (Expense) Benefit	34	43	56
Actuarial (losses) gains arising during the period, Tax (Expense) Benefit	12	(23)	(39)
Net decrease in unrealized gains, net, Tax (Expense) Benefit	46	20	17
Post-retirement unfunded health benefit: Net of Tax Amount
Reclassification adjustment for gains realized in net income, Net of Tax Amount	(98)	(67)	(88)
Actuarial (losses) gains arising during the period, Net of Tax Amount	(34)	38	63
Net decrease in unrealized gains, net, Net of Tax Amount	(132)	(29)	(25)
Other comprehensive (loss) income, Before-tax Amount	(43,447)	1,408	(42,018)
Other comprehensive (loss) income, Tax (Expense) Benefit	11,252	(503)	16,178
Net current period other comprehensive income (loss)	(32,195)	905	(25,840)
Comprehensive income, Net of Tax Amount	$ 396,281	$ 276,379	$ 220,944