Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in accumulated other comprehensive income (loss), net of tax
Balance	$ 1,242,356	$ 1,259,274	$ 1,083,981
Other comprehensive (loss) gain, net of tax	(3,667)	(3,551)	1,774
Balance	1,588,552	1,242,356	1,259,274
Accumulated Other Comprehensive Income/(Loss)
Changes in accumulated other comprehensive income (loss), net of tax
Balance	(16,734)	(13,183)	(14,957)
Other comprehensive income (loss) before reclassifications	(4,544)
Amounts reclassified from accumulated other comprehensive gain	877
Other comprehensive (loss) gain, net of tax	(3,667)
Balance	(20,401)	(16,734)	$ (13,183)
Defined Benefit Pension Plan
Changes in accumulated other comprehensive income (loss), net of tax
Balance	(6,957)
Other comprehensive income (loss) before reclassifications	826
Amounts reclassified from accumulated other comprehensive gain	877
Other comprehensive (loss) gain, net of tax	1,703
Balance	(5,254)	(6,957)
Foreign Currency Translation Losses
Changes in accumulated other comprehensive income (loss), net of tax
Balance	(9,858)
Other comprehensive income (loss) before reclassifications	(5,296)
Other comprehensive (loss) gain, net of tax	(5,296)
Balance	(15,154)	(9,858)
Unrealized Gains and (Losses) on Available-for-Sale Securities
Changes in accumulated other comprehensive income (loss), net of tax
Balance	81
Other comprehensive income (loss) before reclassifications	(74)
Other comprehensive (loss) gain, net of tax	(74)
Balance	$ 7	$ 81