Goodwill and Other Intangible Assets - Summary of gross carrying amounts - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Other intangible assets
Gross carrying amount	$ 82,154	$ 82,155	$ 82,154	$ 82,155	$ 82,154
Accumulated amortization	(40,416)	(32,173)	(40,416)	(32,173)	(34,729)
Net carrying amount	41,738	49,982	41,738	49,982	$ 47,425
Amortization expense	1,891	$ 2,078	5,687	$ 6,058
Estimated amortization expense for other intangibles for each of the next five quarters
December 31, 2016	1,890		1,890
March 31, 2017	1,810		1,810
June 30, 2017	1,798		1,798
September 30, 2017	1,797		1,797
December 31, 2017	1,797		1,797
Thereafter	$ 32,646		$ 32,646
Minimum
Other intangible assets
Estimated useful lives			2 years
Maximum
Other intangible assets
Estimated useful lives			15 years