Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Oct. 21, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Trading Symbol	GLT
Entity Registrant Name	GLATFELTER P H CO
Entity Central Index Key	0000041719
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity File Number	1-03560
Entity Tax Identification Number	230628360
Entity Address, Address Line One	96 South George Street
Entity Address, Address Line Two	Suite 520
Entity Address, City or Town	York
Entity Address, State or Province	Pennsylvania
Entity Address, Postal Zip Code	17401
City Area Code	717
Local Phone Number	850-0170
Entity Common Stock, Shares Outstanding		44,171,151