In thousands of dollars | |||||||||
2013 | 2012 | 2011 | |||||||
Service cost—benefits earned during the period | $ | 7,538 | $ | 7,545 | $ | 7,833 | |||
Interest cost on benefit obligation | 141,030 | 155,376 | 171,339 | ||||||
Expected return on plan assets | (198,216 | ) | (189,863 | ) | (211,659 | ) | |||
Amortization of prior service costs | 7,566 | 7,689 | 7,580 | ||||||
Amortization of actuarial loss | 63,212 | 53,429 | 37,901 | ||||||
Pension expense for company-sponsored retirement plans | 21,130 | 34,176 | 12,994 | ||||||
Settlement and special termination benefit charge | 3,077 | 7,946 | 1,068 | ||||||
Total pension cost | $ | 24,207 | $ | 42,122 | $ | 14,062 | |||