Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 127,491	$ 116,750	$ 94,115
Other comprehensive (loss) income, net of tax
Unrealized (losses) gains on securities	(5,847)	16,028	(38,065)
Pension and other postretirement benefits	7,708	(29,755)	16,752
Other comprehensive (loss) income	1,861	(13,727)	(21,313)
Comprehensive income	$ 129,352	$ 103,023	$ 72,802