Net Carrying Value of Goodwill (Details) - USD ($) $ in Thousands		Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Gross carrying value of goodwill and the accumulated impairment charge
Gross carrying value		$ 217,970		$ 187,212
Accumulated impairment charge	[1]	(40,159)		(40,159)
Net carrying value		$ 177,811	$ 147,053	$ 147,053	$ 140,638	$ 140,638	$ 140,638

[1] A goodwill impairment charge was recognized in 2011 and was due to high levels of volatility and dislocation in bank stock prices nationwide.