Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income	$ 164,947	$ 217,049	$ 369,873
Other comprehensive (loss) income, net of tax:
Foreign currency translation reclassification adjustment included in net income			2,266
Unrealized (losses) gains on marketable securities:
Unrealized (losses) gains on marketable securities arising during period, net of tax of $216, $370, $1,247	(1,097)	2,009	1,409
Less: Reclassification adjustment for gains included in net income, net of tax of $(257), $(201), $(581)	(447)	(702)	(1,412)
Total unrealized gain (loss) on marketable securities	(1,544)	1,307	(3)
Defined benefit pension and post-retirement plans:
Amortization of prior service (benefit) cost included in net periodic pension and post-retirement expense/income, net of tax $(159), $(134), $9	(276)	(233)	14
Other comprehensive (loss) income	(1,820)	1,074	2,277
Comprehensive income	$ 163,127	$ 218,123	$ 372,150