Accumulated Other Comprehensive Loss (Reclassifications out of AOCI) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Long-term obligations	$ 179,183		$ 215,356		$ 563,593		$ 651,740
Securities gains (losses)	0		31		0		(11)
Reclassification adjustment for losses included in income before income taxes	4,298		2,788		12,896		8,368
Amounts reclassified from accumulated other comprehensive income, net of tax	2,668	[1]	2,142	[1]	8,887	[1]	6,458	[1]
Unrealized Loss on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Long-term obligations	(831)	[1]	(769)	[1]	(2,463)	[1]	(2,294)	[1]
Income taxes	400	[1]	304	[1]	1,044	[1]	906	[1]
Amounts reclassified from accumulated other comprehensive income, net of tax	431	[1],[2]	465	[1],[2]	1,419	[1],[2]	1,388	[1],[2]
Unrealized Gains on Investment Securities Available for Sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Securities gains (losses)	0	[1]	31	[1]	0	[1]	34	[1]
Income taxes	0	[1]	(12)	[1]	0	[1]	(13)	[1]
Amounts reclassified from accumulated other comprehensive income, net of tax	0	[1],[2]	(19)	[1],[2]	0	[1],[2]	(21)	[1],[2]
Defined Benefit Pension Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Employee Benefits, prior service costs	(53)	[1]	(53)	[1]	(158)	[1]	(158)	[1]
Reclassification adjustment for losses included in income before income taxes	(4,245)	[1]	(2,735)	[1]	(12,738)	[1]	(8,210)	[1]
Total before taxes	(4,298)		(2,788)	[1]	(12,896)		(8,368)	[1]
Income taxes	2,061	[1]	1,092	[1]	5,428	[1]	3,277	[1]
Amounts reclassified from accumulated other comprehensive income, net of tax	$ 2,237	[1],[2]	$ 1,696	[1],[2]	$ 7,468	[1],[2]	$ 5,091	[1],[2]

[1] Amounts in parentheses indicate debits to profit/loss.Details about accumulated other comprehensive loss Amount reclassified from accumulated other comprehensive loss1 Affected line item in the statement where net income is presented (dollars in thousands) Nine months ended September 30, 2013 Gains and losses on cash flow hedges Interest rate swap contracts $(2,463) Long-term obligations 1,044 Income taxes $(1,419) Net incomeUnrealized gains and losses on available for sale securities $— Securities gains (losses) — Income taxes $— Net incomeAmortization of defined benefit pension items Prior service costs $(158) Employee benefits Actuarial gains (12,738) Employee benefits (12,896) Income before income taxes 5,428 Income taxes $(7,468) Net incomeTotal reclassifications for the period $(8,887) Nine months ended September 30, 2012 Gains and losses on cash flow hedges Interest rate swap contracts $(2,294) Long-term obligations 906 Income taxes $(1,388) Net income Unrealized gains and losses on available for sale securities $34 Securities gains (losses) (13) Income taxes $21 Net income Amortization of defined benefit pension items Prior service costs $(158) Employee benefits Actuarial gains (8,210) Employee benefits (8,368) Income before income taxes 3,277 Income taxes $(5,091) Net incomeTotal reclassifications for the period $(6,458) 1 Amounts in parentheses indicate debits to profit/loss.

[2] All amounts are net of tax. Amounts in parentheses indicate debits.