Consolidated Statements of Comprehensive Income (Unaudited) - 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		$ 30,628	$ 31,118	$ 65,853	$ 58,673
Other comprehensive income (loss), net of tax
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax		5,445	(1,924)	10,174	(7,392)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax		8,590	(112)	11,875	103
Net change in other comprehensive income for defined benefit postretirement plans	[1]	40	117	80	234
Total other comprehensive income (loss)		14,075	(1,919)	22,129	(7,055)
Total comprehensive income		$ 44,703	$ 29,199	$ 87,982	$ 51,618

[1] The amortization of prior service costs is included in the computation of net periodic pension cost as disclosed in the Employee Benefit Plans footnote in the Company's Annual Report on Form 10-K for the year ended December 31, 2018, filed with the Securities and Exchange Commission.