Authoritative Accounting Guidance New Accounting Pronouncements and Changes in Accounting Principles (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Investments	Dec. 31, 2013	Dec. 31, 2012
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of Investments in Other Assets, Noncurrent	4
Current Income Tax Expense (Benefit)	$ 39,869	$ 35,290	$ 21,276
Accounting Standards Update 2014-01 [Member] | Investment in Affordable Housing Projects [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
2015	6,943
2016	37
2017	37
2018	37
2019	37
2020	37
2021	37
2022	0
2023	26
Accounting Standards Update 2014-01 [Member] | Investment in Affordable Housing Projects [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other Assets, Miscellaneous	5,084
Current Income Tax Expense (Benefit)	$ (27)