Goodwill and Other Intangible Assets - Summary of gross carrying amounts - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Other intangible assets
Gross carrying amount	$ 100,274	$ 82,154	$ 100,274	$ 82,154	$ 82,154
Accumulated amortization	(49,802)	(40,416)	(49,802)	(40,416)	(42,306)
Net carrying amount	50,472	41,738	50,472	41,738	$ 39,848
Amortization expense	2,494	1,891	7,496	5,687
Amortization of Intangible Assets	2,494	$ 1,891	7,496	$ 5,687
Estimated amortization expense for other intangibles for each of the next five quarters
December 31, 2017	2,494		2,494
March 31, 2018	2,331		2,331
June 30, 2018	2,319		2,319
September 30, 2018	2,318		2,318
December 31, 2018	2,317		2,317
Thereafter	$ 38,693		$ 38,693
Minimum
Other intangible assets
Estimated useful lives			2 years
Maximum
Other intangible assets
Estimated useful lives			15 years