- Changes in Outstanding Common Stock (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Outstanding, beginning of year (in shares)	104,572	99,843	99,377
Shares issued upon exercise of options (in shares)	603	416	125
Shares issued for time vested restricted stock (net of cancellations) (in shares)	1,188	952	341
Shares issued for acquisition (in shares)	0	3,361	0
Outstanding, end of year (in shares)	106,363	104,572	99,843