Employee Benefit Plans - Summary of funded status of Retirement Income Plan and amounts recognized in consolidated balance sheets (Details) (Retirement Income Plan, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Retirement Income Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation at end of year	$ 37,528	$ 42,699
CHANGE IN PROJECTED BENEFIT OBLIGATION:
Benefit obligation at beginning of year	42,699	38,278
Service cost
Interest cost	1,741	1,869	1,916
Amendments
Actuarial loss	(5,199)	4,221
Benefits paid	(1,713)	(1,669)
Projected benefit obligation at end of year	37,528	42,699	38,278
CHANGE IN PLAN ASSETS:
Fair value of plan assets at beginning of year	29,519	24,180
Actual return on plan assets	3,820	2,712
Employer contribution	800	4,296
Benefits paid	(1,713)	(1,669)
Fair value of plan assets at end of year	32,426	29,519	24,180
Funded status at end of year	(5,102)	(13,180)
AMOUNTS RECOGNIZED IN THE CONSOLIDATED BALANCE SHEETS CONSIST OF:
Noncurrent assets
Current liabilities
Noncurrent liabilities	(5,102)	(13,180)
Amounts recognized in balance sheet	(5,102)	(13,180)
AMOUNTS (PRE-TAX) RECOGNIZED IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) CONSIST OF:
Net loss (gain)	15,369	23,129
Prior service cost (credit)
Net transition obligation (asset)
Before-tax amount	$ 15,369	$ 23,129