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	$ 333,562	$ 229,264	$ 200,274
Investment securities available for sale
Net unrealized gains (losses)	(39,891)	(12,302)	(17,900)
Net unrealized gain (loss) on available for sale securities transferred to held to maturity securities	0	(14,738)	0
Amortization of net unrealized gain (loss) on available for sale securities transferred to held to maturity securities	(572)	(2,665)	(5,887)
Reclassification adjustment for net losses (gains) realized in net income (a)	1,985	0	(9,316)
Reclassification from OCI due to change in accounting principle	(84)	0	0
Reclassification of certain tax effects from OCI	(8,419)	0	0
Income tax (expense) benefit	9,791	11,331	12,565
Other comprehensive income (loss) on investment securities available for sale	(37,189)	(18,374)	(20,538)
Defined benefit pension and postretirement obligations
Amortization of prior service cost	(148)	(148)	(73)
Plan amendments	0	0	1,759
Net actuarial (loss) gain	(28,612)	14,273	(6,141)
Amortization of actuarial loss (gain)	2,203	2,282	2,115
Reclassification of certain tax effects from OCI	(5,235)	0	0
Income tax (expense) benefit	6,767	(6,112)	815
Other comprehensive income (loss) on pension and postretirement obligations	(25,025)	10,295	(1,525)
Total other comprehensive income (loss)	(62,214)	(8,079)	(22,063)
Comprehensive income	$ 271,348	$ 221,185	$ 178,211

Amortization of Net Unrealized Gain on Available-for-Sale Securities Transfered to Held-to-maturity Securities

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Other Comprehensive Income Loss Reclassification Adjustment From AOCI Defined Benefits Tax Effect BeforeTax

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