Pension Plans and Other Postretirement Benefits (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Qualified Defined Contribution Plan [Member]
Summary of contributions to qualified defined contribution plan, 401(k), non-qualified defined contribution plan and total assets of the plans
Contributions to employees’ accounts	$ 4,701	$ 4,148	$ 4,864
Total assets at the end of the year	135,097	141,286	149,675
401 K Plan [Member]
Summary of contributions to qualified defined contribution plan, 401(k), non-qualified defined contribution plan and total assets of the plans
Contributions to employees’ accounts	2,781	2,753	2,856
Total assets at the end of the year	134,891	118,073	111,370
Non Qualified Defined Contribution Plan [Member]
Summary of contributions to qualified defined contribution plan, 401(k), non-qualified defined contribution plan and total assets of the plans
Contributions to employees’ accounts	0	0	0
Total assets at the end of the year	$ 0	$ 0	$ 0