Restricted Cash (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Restricted Cash and Cash Equivalents Items [Line Items]
Cash	$ 2,186	$ 2,294	$ 2,166	$ 2,218
Comerica Bank [Member] | Colorado [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Letters of credit outstanding, amount	$ 185	$ 242