CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net loss arising from period related to defined benefit pension plan, tax	$ 0	$ 0	$ 0	$ (119)
Amortization of prior service cost included in net periodic pension cost, tax	0	0	0	28
Partial settlement of pension plan liability, tax	0	0	0	336
Unrealized gains (losses) on change in fair value of interest rate swap contracts, tax	0	199	110	549
Reclassification adjustment for (gains) losses included in net income, tax	$ 0	$ (101)	$ (55)	$ (280)