Leases (Details) ft² in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) ft²	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Operating Leased Assets [Line Items]
Lease rental expense incurred	$ 16,900	$ 16,500	$ 15,800
Future minimum lease payments	65,892
Future minimum lease payments, Year 1	12,516
Future minimum lease payments, Year 2	9,901
Future minimum lease payments, Year 3	9,178
Future minimum lease payments, Year 4	6,961
Future minimum lease payments, Year 5	6,132
Future minimum lease payments, Thereafter	$ 21,204
Lease Agreement Effective September 14, 2012 | Canonsburg Office, New Company Headquarters
Operating Leased Assets [Line Items]
Area of real estate property | ft²	186
Period of leased property	183 months
Base rent, years one through five	$ 4,300
Base rent, years six through ten	4,500
Base rent, years eleven through fifteen	4,700
Lease rental expense incurred	$ 4,400	$ 4,400	800
Amended Lease Agreement Effective January 1, 2004 | Canonsburg Office
Operating Leased Assets [Line Items]
Lease rental expense incurred			$ 1,400