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Business Segments, Concentration of Business, and Credit Risk and Significant Customers - Total Assets from Reportable Segments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reconciliations of total assets from reportable segments to the condensed consolidated balance sheets
Cash and cash equivalents	$ 225,143	$ 245,088	$ 237,125	$ 110,247	$ 263,606
Unallocated deferred tax assets	29,083us-gaap_DeferredTaxAssetsNet	38,933us-gaap_DeferredTaxAssetsNet	35,632us-gaap_DeferredTaxAssetsNet
Total assets	1,169,933us-gaap_Assets	1,064,204us-gaap_Assets	1,259,729us-gaap_Assets
Reportable segments
Reconciliations of total assets from reportable segments to the condensed consolidated balance sheets
Total assets	698,174	654,679	801,796	816,807
Unallocated to Segments
Reconciliations of total assets from reportable segments to the condensed consolidated balance sheets
Other unallocated corporate assets	$ 217,533	$ 125,504	$ 185,176