Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income		$ 165,175	$ 121,622	$ 87,204
Other comprehensive income (loss), net of tax
Net change in fair value of securities available for sale		10,345	(4,501)	(677)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax		10,331	4,829	443
Net change in other comprehensive income for defined benefit postretirement plans	[1]	(1,334)	1,558	(260)
Total other comprehensive income (loss)		19,342	1,886	(494)
Total comprehensive income		$ 184,517	$ 123,508	$ 86,710

[1] The amortization of prior service costs is included in the computation of net periodic pension costs as disclosed in Note 15 - Employee Benefit Plans.