Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 111,511	$ 126,452	$ 118,352
Other comprehensive income (loss), before tax:
Unrealized gains (losses) arising during the period	1,920	(20,231)	23,172
Amount reclassified from accumulated other comprehensive loss	88	(235)	204
Total Minimum pension liability	2,008	(20,466)	23,376
Income tax (expense) benefit related to items of comprehensive income	(724)	3,254	(7,892)
Other comprehensive income (loss), net of tax	1,284	(17,212)	15,484
Comprehensive income	$ 112,795	$ 109,240	$ 133,836