Summary of Significant Accounting Policies Effects of Revision (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent	$ 27,189	$ 25,655	$ 22,337	$ 28,933	$ 33,920	$ 40,092
Assets	768,164	678,479	649,264	591,908	552,423	499,050
Additional Paid in Capital	676,605	628,034	607,240	594,489	585,648	565,946
Stockholders' Equity Attributable to Parent	602,165	531,065	490,781	462,864	435,156	404,173
Scenario, Previously Reported [Member]
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent		17,612		22,945	28,546	38,024
Assets		670,436		585,920	547,049	496,982
Additional Paid in Capital		619,991		588,501	580,274	563,878
Stockholders' Equity Attributable to Parent		523,022		456,876	429,782	402,105
Scenario, Adjustment [Member]
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent		8,043		5,988	5,374	2,068
Assets		8,043		5,988	5,374	2,068
Additional Paid in Capital		8,043		5,988	5,374	2,068
Stockholders' Equity Attributable to Parent		$ 8,043		$ 5,988	$ 5,374	$ 2,068