Changes in Stockholders' Equity (Narrative) (Details) shares in Millions	Mar. 31, 2017 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase program, outstanding balance authorized to be repurchased	$ 331,400,000
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased | shares	31.4
December 2016 ASR Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Repurchase Program, Authorized Amount	$ 300,000,000