Pension and Retirement Plans, Deferred Compensation Arrangement with Individual, Postretirement Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Company's 401(K) contributions for the year	$ 5,292	$ 5,134	$ 4,941
SERP [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Change in the fair market value of Company stock held in the SERP	241	74	$ 601
Cost [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Plan Assets	5,180	6,297
Cost [Member] | Company Stock [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Plan Assets	1,778	2,929
Cost [Member] | Equity Securities [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Plan Assets	3,402	3,368
Market [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Plan Assets	5,869	8,128
Market [Member] | Company Stock [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Plan Assets	2,560	4,401
Market [Member] | Equity Securities [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Plan Assets	$ 3,309	$ 3,727