Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 84,661	$ 89,192	$ 171,347	$ 158,648
Investment securities available for sale
Net unrealized gains (losses)	59,476	(18,919)	89,966	(60,754)
Amortization of net unrealized gain (loss) on available for sale securities transferred to held to maturity securities	218	(335)	288	(632)
Reclassification adjustment for net losses (gains) realized in net income(a)	(463)	2,015	(2,143)	2,015
Reclassification from OCI due to change in accounting principle	0	0	0	(84)
Reclassification of certain tax effects from OCI	0	0	0	(8,419)
Income tax (expense) benefit	(14,940)	4,705	(22,242)	15,340
Other comprehensive income (loss) on investment securities available for sale	44,292	(12,533)	65,869	(52,533)
Defined benefit pension and postretirement obligations
Amortization of prior service cost	(38)	(38)	(75)	(76)
Amortization of actuarial loss (gain)	64	465	128	929
Reclassification of certain tax effects from OCI	0	0	0	(5,235)
Income tax (expense) benefit	(7)	(109)	(13)	(216)
Other comprehensive income (loss) on pension and postretirement obligations	20	318	40	(4,597)
Total other comprehensive income (loss)	44,311	(12,215)	65,909	(57,130)
Comprehensive income	$ 128,972	$ 76,977	$ 237,256	$ 101,518

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

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