Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income	$ 56,931	$ 53,291	$ 44,478
Other comprehensive income (loss)
Foreign currency translation adjustment	(90)	(1,688)	(150)
Net actuarial loss arising during the period	(3,322)	(7,878)	(695)
Less: amortization of net actuarial loss included in net periodic cost for retirement plans	2,098	1,551	1,236
Settlement charge included in net periodic cost for retirement plans			1,222
Retirement liabilities - before tax	(1,224)	(6,327)	1,763
Income tax (expense) benefit	482	2,474	(691)
Retirement liabilities - after tax	(742)	(3,853)	1,072
Other comprehensive income (loss), net of tax	(832)	(5,541)	922
Comprehensive income	$ 56,099	$ 47,750	$ 45,400