Consolidated Statements of Comprehensive Income - AOCI - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		$ 2,054,998	$ 1,864,874	$ 1,257,080
Other comprehensive (loss) income		50,558	(12,787)	7,874
Adjustments to apply recent accounting pronouncements	[1]				$ 0
Ending balance		2,370,793	2,054,998	1,864,874
Accumulated Unrealized Loss on Securities Available- for-Sale
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(28,792)	(13,976)	(22,645)
Other comprehensive (loss) income		44,600	(11,952)	8,669
Adjustments to apply recent accounting pronouncements	[1]				(2,864)
Ending balance		15,808	(28,792)	(13,976)
Accumulated Unrealized Loss on Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(3,763)	(1,176)
Other comprehensive (loss) income			1,997	(2,587)
Adjustments to apply recent accounting pronouncements	[1]				(784)
Ending balance				(3,763)
Accumulated Unrealized Loss on Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(2,550)
Other comprehensive (loss) income		3,369
Ending balance		819	(2,550)
Unrecognized Net Pension Costs
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(21,170)	(15,297)	(17,089)
Other comprehensive (loss) income		2,589	(2,832)	1,792
Adjustments to apply recent accounting pronouncements	[1]				(3,041)
Ending balance		(18,581)	(21,170)	(15,297)
Total Accumulated Other Comprehensive Loss, Net of Tax
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(52,512)	(33,036)	(40,910)
Other comprehensive (loss) income		50,558	(12,787)	7,874
Adjustments to apply recent accounting pronouncements	[1]				$ (6,689)
Ending balance		$ (1,954)	$ (52,512)	$ (33,036)

[1] As a result of accounting guidance adopted in 2018, certain reclassifications were made from accumulated other comprehensive loss to retained earnings as of January 1, 2018. For further discussion of this guidance, see Note 2. "Recent Accounting Pronouncements." ⁽²⁾As a result of accounting guidance adopted in 2019, the remaining deferred gain on a sale-leaseback transaction was recognized as a cumulative-effect adjustment to retained earnings as of January 1, 2019. For further discussion of this guidance, see Note 2, "Recent Accounting Pronouncements."