Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 132,728	$ 127,491	$ 116,750
Other comprehensive (loss) income, net of tax
Unrealized (losses) gains on securities	(7,897)	(5,847)	16,028
Pension and other postretirement benefits	(1,215)	7,708	(29,755)
Other comprehensive (loss) income	(9,112)	1,861	(13,727)
Comprehensive income	$ 123,616	$ 129,352	$ 103,023