Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Tax expense (benefit) on unrealized gain (loss) on derivatives	$ 66	$ 34	$ (32)
Tax expense (benefit) on unrealized gain (loss) on investments	(17)	29	(8)
Tax expense (benefit) on pension and other post-retirement benefits liability adjustment	$ 6,419	$ 2,469	$ (9,678)