Leases (Details) ft² in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) ft²	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Operating Leased Assets [Line Items]
Lease rental expense incurred	$ 16,500	$ 15,800	$ 14,100
Future minimum lease payments	71,887
Future minimum lease payments, Year 1	13,800
Future minimum lease payments, Year 2	10,449
Future minimum lease payments, Year 3	7,834
Future minimum lease payments, Year 4	7,043
Future minimum lease payments, Year 5	6,195
Future minimum lease payments, Thereafter	$ 26,566
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	800
Amended Lease Agreement Effective January 1, 2004 | Canonsburg Office
Operating Leased Assets [Line Items]
Lease rental expense incurred		$ 1,400	$ 1,400